Craig Edwards on tue 16 mar 04
Hello Roger:
I know that you mean well and all but your experiment is not univesally
true. Simply put hydrometers work well for solutions, not in a
suspension of colloids and, or crystalloids in a liquid. The major
factor involved is what is called the yield strength(yield value). The
hydrometer is prevented from sinking to the depth required by the fluid
density depending on the yield strength of the suspension. This has been
documented and thoroughly tested. Check your Ceramic Glazes, by
Parmelee. He explains in vivid detail, very interesting reading. Pages
121-124 third edition.
Cheers
Craig Edwards
New London MN
Roger Graham wrote:
>Been off-list for some time, drowned in spam. Last night checked the
>archives for the last few weeks of posts. Shock, horror. The anti-hydrometer
>lobby is at it again. Somebody asked an innocent question about using a
>hydrometer to measure specific gravity of a glaze. Lots of replies appeared,
>telling why it's not a good idea. Dogmatic statements that hydrometers are
>"notoriously inaccurate".
>
>All this stuff came up fifteen months ago (December 2002). The
>anti-hydrometer statements disturbed me then, and disturb me now. It's just
>not true. Well-meant advice says hydrometers don't work. Simple experiment
>shows they do, and quite accurately too. I wrote a long post giving details
>at the time (Hydrometers... the case for the defence). Met with a deafening
>silence. Don't let experimental results conflict with authority or argument.
>Don't confuse me with facts, my mind is made up.
>
>
>
Kathi LeSueur on wed 17 mar 04
Hydrometers may not be the ideal for measuring viscosity. But it sure
beats nothing. You have to be a pretty experienced glazer to just dip
your finger in the glaze to know if it's right. And, I'm not sure that
an experience glazer can tell all that well.
Kathi
Craig Edwards on wed 17 mar 04
Des: The point is that many times it is not reproducible in the same lab
time and time again due to "the viscous properties of the slip falsify
the readings of the instrument: changes in the physical conduct of the
glaze due to solution, growth of algae, bacteria, chemical reactions,
and temperature changes accompanying a period of aging, may be of very
great importance." to quote Parmelee and Harman.
This has also been my experience that hydrometer readings will vary over
time due to all of the above, which affect the yield and mobility of a
glaze.
Wouldn't it be more prudent to test the mobility of the glaze instead of
the SP?
Cheers
Craig Edwards
New London MN
Des & Jan Howard wrote:
>Craig
>The whole point is that it does not have to be universally true
>& reproducible in anothers lab.
>This is the viewpoint of the scientist, I take the viewpoint of the engineer,
>can I get it to do the same thing, here, tomorrow, next week.
>When direct experience flies in the face of authority at any level I give authority the flick.
>Des
>
>
>
>
>
Earl Krueger on wed 17 mar 04
On Mar 17, 2004, Carol Tripp wrote:
> Regarding the "are hydrometers used in glazes to measure specific
> gravity
> accurate debate" - isn't it simply a matter of consistant measuring
> time
> after time after time?
Carol,
Since many of the experts are now out partying, or sleeping
it off, they may have no inclination, nor be in condition, to give
a rational answer so I will take a at this one.
In my opinion you have hit on the crux of the whole problem.
With certain glazes the flow of slurry around the hydrometer
is probably no longer "frictionless" as it would appear to be in
plain water or a low density mix. Forces other than gravity
come into play which affect how far the hydrometer sinks
thereby affecting the reading.
These "other forces" could be dependent on factors such as
how long the glaze has been sitting without stirring. I would
guess that if one stirred a flocculated glaze vigorously and
then took hydrometer readings every 5 minutes the readings
would change over time. In other words the readings would
NOT be consistent.
Just my guess.
Earl K...
Bothell, WA, USA
Roger Graham on wed 17 mar 04
Been off-list for some time, drowned in spam. Last night checked the
archives for the last few weeks of posts. Shock, horror. The anti-hydrometer
lobby is at it again. Somebody asked an innocent question about using a
hydrometer to measure specific gravity of a glaze. Lots of replies appeared,
telling why it's not a good idea. Dogmatic statements that hydrometers are
"notoriously inaccurate".
All this stuff came up fifteen months ago (December 2002). The
anti-hydrometer statements disturbed me then, and disturb me now. It's just
not true. Well-meant advice says hydrometers don't work. Simple experiment
shows they do, and quite accurately too. I wrote a long post giving details
at the time (Hydrometers... the case for the defence). Met with a deafening
silence. Don't let experimental results conflict with authority or argument.
Don't confuse me with facts, my mind is made up.
To repeat briefly, I've been relying on a hydrometer to measure SG of glazes
for years. Disturbed by all the anti-hydrometer statements, it seemed wise
to re-measure and check. I chose 4 glazes from the stock of 20 or so
routinely used here. Carefully measured the specific gravity of each one,
using the conventional "relative density bottle" method, as accurately as
possible. Then measured them all again using the hydrometer. All the boring
details of weights etc are in the original post, but here's a summary:
Talc White glaze, SG by weighing 1.42, SG by hydrometer 1.4, difference
about 2 percent
Indian Red glaze, SG by weighing 1.29, SG by hydrometer 1.32, difference
about 2 percent.
Speckle Matt glaze, thin and watery, SG by weighing 1.28, SG by hydrometer
1.29, difference about 1percent
Copper Red glaze, dense and creamy, SG by weighing 1.49, SG by hydrometer
1.48, difference about 1 percent.
Those are the figures, by experiment. A 20-second measurement with a
hydrometer can be as good as a messy 5-minute measurement with scales nd a
bottle. Hydrometers aren't as unreliable as some of the posts would have
you believe. Sure, they aren't a big success for creamy slip or very
viscous clinging glaze, but for ordinary glaze mixes they work just fine. If
the glaze is thin and watery, the hydrometer sinks to its own level, the
same level every time, without being dragged or retarded by the liquid. If
the glaze is a bit more thick and creamy, just tap the side of the container
to agitate the liquid a bit and the hydrometer will sink to its true level.
You don't need to buy a fancy expensive instrument. Making and calibrating
your own is no big deal, starting with a MacDonalds drinking straw. Email me
off list and I can return a one-page pdf file with instructions and a
calibration chart. The same page appears on Des Howard's website
(http://www.luepottery.hwy.com.au).
Hydrometers aren't as unreliable as they're often made out to be. Trust me.
Or better still, make a hydrometer and check it out for yourself.
Roger Graham, near Gerringong, Australia
http://members.optusnet.com.au/~rogergraham
Dewitt on thu 18 mar 04
At 01:42 AM 3/18/2004, you wrote:
>With certain glazes the flow of slurry around the hydrometer
>is probably no longer "frictionless" as it would appear to be in
>plain water or a low density mix. Forces other than gravity
>come into play which affect how far the hydrometer sinks
>thereby affecting the reading.
Just a guess, but I suspect that a hydrometer with a higher mass would
yield more consistent results in a glaze than one with a lower mass - i.e.,
a homemade hydrometer made with a dowel and fish weight might work better
than a lightweight commercial one.
deg
Ivor and Olive Lewis on thu 18 mar 04
Dear Carol,
When measuring there are two things to consider, Accuracy and
Precision.
They mean different things. Both contribute and both are essential.
If we hit the "Bull" of the darts board with three darts we are
accurate and precise. If we aim for the "bull" and all the darts plant
in the "double One" we are precise but inaccurate. If you aim for the
"Bull" and they scatter around the board then there is neither
precision nor accuracy. Accuracy and imprecision is not an option.
It is not unusual when using instruments to take several readings and
take the average. I step onto the scales five times even though I am
only concerned with the change over time.
In the case of the Hydrometer I suggest the measurement should be done
five times and the instrument. even if it is a makeshift one, should
be cleaned before each recorded event and the slop should be restirred
if we are aiming for a degree of precision. Accuracy of an instrument
depends on many factors. But I agree with you, a home made instrument
used in a consistent way will give results that can give good guidance
to its user.
Best regards,
Ivor Lewis. Redhill, South Australia
Carol Tripp on thu 18 mar 04
Regarding the "are hydrometers used in glazes to measure specific gravity
accurate debate" - isn't it simply a matter of consistant measuring time
after time after time? What I mean is, my bathroom scale may not be
accurate but it shows gains and losses in my weight time after time. I may
be in for a shock at the doctor's office when her scale shows me that I am 2
kgs fatter but that doesn't really matter (well it does but that's besides
the point). If you use the same instrument, a homemade hydrometer for
example, to measure your glazes in your studio won't you end up with the
information you need to mix batches of consistant thickness/thinness? Just
note your numbers. Does it really matter if the hydrometer is not up to lab
standard?
I am just asking...
Best regards,
Carol
Dubai, UAE
_________________________________________________________________
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Ivor and Olive Lewis on thu 18 mar 04
Dear Kathi LeSueur,
You say <>
And there I thought they measured fluid density.
I was wondering why wine and beer flowed so freely at conferences. Now
I know!!
Best regards,
Ivor Lewis. Redhill, South Australia
Michael McDowell on thu 18 mar 04
Craig,
I know that you have cited Parmelee, and that should be the end of
discussion, but I feel for poor Roger sticking his neck out about
this only to have the weight of "Authority" dropped on him this way.
I'm sure he will continue to use a hydrometer in his own shop
practices however. He has clearly and convincingly demonstrated and
"documented" to us that a hydrometer is a useful aproximately
accurate indicator of the specific gravity of the glazes he is
using. Inaccuracy there may be, but within the range that many of us
are working it is inaccuracy of an acceptible degree for the
convenience.
I just felt that Roger might like to hear that he is not alone in
continuing to make use of this device. And to throw in my little
shop hint for reducing "drag" of the mixture on the instrument. My
pratice is to always dip the hydrometer first in clean water, then
immediately in the glaze to be measured. This seems to provide a
little lubrication for the float to more easily find its level in
the mixture. I'll use glazes with specific gravities up to 1.6, and
get useful, repeatable readings on my hydrometer. Thanks for the
warning that I am in error to rely on this tool though. There may
come a time when that knowledge is useful to me too!
Michael McDowell
Whatcom County, WA
Michael@McDowellPottery.com
http://www.McDowellPottery.com
Des & Jan Howard on thu 18 mar 04
Craig
The whole point is that it does not have to be universally true
& reproducible in anothers lab.
This is the viewpoint of the scientist, I take the viewpoint of the engineer,
can I get it to do the same thing, here, tomorrow, next week.
When direct experience flies in the face of authority at any level I give authority the flick.
Des
Craig Edwards wrote:
> Hello Roger:
> I know that you mean well and all but your experiment is not univesally
> true. Simply put hydrometers work well for solutions, not in a
> suspension of colloids and, or crystalloids in a liquid. The major
> factor involved is what is called the yield strength(yield value). The
> hydrometer is prevented from sinking to the depth required by the fluid
> density depending on the yield strength of the suspension. This has been
> documented and thoroughly tested. Check your Ceramic Glazes, by
> Parmelee. He explains in vivid detail, very interesting reading. Pages
> 121-124 third edition.
--
Des & Jan Howard
Lue Pottery
LUE NSW 2850
Australia
Ph/Fax 02 6373 6419
http://www.luepottery.hwy.com.au
Lee Love on thu 18 mar 04
Carol Tripp wrote:
> Does it really matter if the hydrometer is not up to lab
> standard?
I don't believe any body is asking for this. They are just pointing
out that you may not be measuring what you think you are measuring.
Lee In Mashiko
Hendrix, Taylor J. on thu 18 mar 04
Carol:
You are right. It matters not a whit what you use for the measurement
as long as you can reproduce it the same way every time. You could make
your own ceramic container for glaze slip weighing too. It doesn't
matter if it's really a pint or not. The problem would only be those
numbers are not portable. You couldn't make suggestions to someone
trying to reproduce your results for example. This is not an issue for
many. Of course one of the benefits of standardized measurements is
that an inch is an inch is an inch is about 2.5 centimeters.
I say use what works for you. Heck use a fish float if you don't want
to buy a hydrometer and you fish. Be warned thought that when your dog
chews up the float, you will have to do all your numbers over again.
Sigh.
Taylor, in Waco
-----Original Message-----
From: Clayart [mailto:CLAYART@LSV.CERAMICS.ORG] On Behalf Of Carol Tripp
Sent: Wednesday, March 17, 2004 9:55 PM
To: CLAYART@LSV.CERAMICS.ORG
Subject: Re: Hydrometers... the case for the defence (again)
Regarding the "are hydrometers used in glazes to measure specific
gravity
accurate debate" - isn't it simply a matter of consistant measuring time
after time after time? =20
...
Craig Edwards on fri 19 mar 04
Hello Ivor: I agree with you that accuracy and precision are goals when
using measuring tools. The main point that has been brought up for using
a hydrometer instead of a graduated cylinder is not accuracy and
precision however but convienence and quickness. It's one of those good
enough types of things.
It seems that 20 seconds is what is wanted for an acceptable time, using
a graduated cylinder it takes me about a minute--I get an accurate
reading. Far to long a time to be acceptable. However I am working on
getting my time better!
Cheers
~Craig Edwards
New London MN
Ivor and Olive Lewis wrote:
>Dear Carol,
>When measuring there are two things to consider, Accuracy and
>Precision.
> Accuracy and imprecision is not an option.
>It is not unusual when using instruments to take several readings and
>take the average. I step onto the scales five times even though I am
>only concerned with the change over time.
>In the case of the Hydrometer I suggest the measurement should be done
>five times and the instrument. even if it is a makeshift one, should
>be cleaned before each recorded event and the slop should be restirred
>if we are aiming for a degree of precision. Accuracy of an instrument
>depends on many factors. But I agree with you, a home made instrument
>used in a consistent way will give results that can give good guidance
>to its user.
>Best regards,
>Ivor Lewis. Redhill, South Australia
>
>
>
Roly Beevor on fri 19 mar 04
Ivor Lewis wrote> When measuring there are two things to consider, Accuracy
and
> Precision.
> They mean different things.
Ivor
Is this an engineering use of the terms, they mean much the same to me?
I'd prefer to think in terms like discrimination, reliability and
reproducibility, and also of suitability for the task.
If someone is using a hydrometer for glaze they want to know whether the
glaze is in the range of thickness which is suitable for the application
technique they are using. If they wanted to take time they could do five
tests, but then they could have got out their measuring cylinder and
balance. The hydrometer is being used as a pass/fail gauge, not for
measuring.
A digital thermometer may give a rather unreliable (several percent off a
true reading) and unreproducible (another thermometer will give a different
temperature) reading of temperature in a kiln, but it has good
discrimination so it can tell you whether the kiln is getting hotter or has
stalled, precise but inaccurate in your terms. The cones are likely to be
less discriminating, if only because they are not easy to see, and to look
at continuously, but show heat work very reliably, is that then imprecise
but accurate?
Ah, semantics.
Roly
Craig Edwards on fri 19 mar 04
Hello Susan: I'm sorry that you took my comments the wrong way. The
original post was a comparision of the hydrometer to pint weight or
graduated cylinder. Hmmm the graduated cylinder is great for small
amounts of slip or glaze, if I might meekly suggest, better than a
hydrometer. (I'm ducking down under the computer desk waiting for
incoming). When I'm working with 50-200gram batches I don't think the
hydrometer will work, that's when using a graduated cylinder and the
gram scale are fine. I have a 100ml and a 50ml. With the 100 ml fill
it with slip and weigh the weight of the slip is your SP times 100. ie
if it weighs 143 ( an old fave of mine) your SP is 1.43.
I'm not sure what floating jars in buckets is all about?
I didn't mean to imply lazy.
I think that the way you have used a hydrometer to get results is
admirable, hardly lazy.
Cheers
~Craig Edwards
New London MN
I think I'll go trim the teabowls that I threw this morning.
Susan Setley wrote:
>In a message dated 3/19/04 10:10:39 AM, craigedwards@CHARTER.NET writes:
>
>
>
>
>>
>>
>
>That's a completely unfair putdown. Some of us didn't even KNOW there was
>another way, and believe it or not, what has been described here as a substitute
>won't even work with everyone -- for instance, because they work with small
>amounts, as I do.
>
>We made a very interesting discovery based on my "good enough" (not lazy)
>approach: while my terra sig is thin, when pieces were accidentally bisqued too
>high, the commercial terra sig peeled off but mine did not. We think mine is
>thin not because there was too much water but because the particles may be
>extremely fine. It may have been a happy accident, and if that is true, I would
>rather have more information about it. But since I only make about 1/2 gallon at
>a time, methods that require floating jars in buckets won't work, while a long
>piece of weighted glass in a tall cylinder will.
>
>It's not laziness, and it's not impatience. Honestly, must we all be so
>hypercritical?
>
>I'm sorry Snail, but "anyone who doesn't do it my way is lazy" is not a fair
>characterization.
>
>
>
Ivor and Olive Lewis on sat 20 mar 04
Dear Roly,
Not Engineering but Science (Careful, critical, systematic thinking if
you wish to be semantic).
Imagine a Darts Board . Three darts. You throw and your darts go into
the Bull, you are accurate and precise. Take another three arrows.
Throw for the Bull. Three projectiles in double one. Now you are
inaccurate but precise. Have pint wile you await your next turn. Fire
three darts at the target. Result, scatter everywhere, all over the
target. You are neither accurate nor precise.
Your example about the digital pyrometer is interesting. In this case
you have to analyse the root causes of the error. Is it in the system
or is it random? or both?
Your example of the Pyrometric cone is interesting. To define both
accuracy and precision in this instance you have to consider the
system and how you would eliminate the errors.
Your example of several pyrometers is interesting since you have to
consider the causes of randomisation.
Results which come up with very close grouping indicate a good degree
of precision. Results which bracket the intended value or point of
interest tell us about accuracy.
Hydrometers measure Fluid Density. A Viscometer measures the rate at
which things will flow. Linear intervals measure "...thickness..."
When you say << ...they want to know whether the glaze is in the range
of thickness which is suitable for the application technique they are
using...>> do you mean "...is this going to flow evenly over the pot
when I dip or when I spray or when I brush..." Or do you mean "... I
will get the coating thickness I need when I dip the pot into this
slop for five seconds..."
Pass/Fail and Go/No Go gauges are very useful tools for quick
discrimination. Once the standard is established there is no need to
for higher skills or knowledge.
The term "Heat Work " is a Tautology". A useful colloquialism never
the less that we can all understand
<<...Ah, semantics... >> Where would we be without words ???
Best regards,
Ivor Lewis. Redhill, South Australia
Ivor and Olive Lewis on sat 20 mar 04
Dear Craig,
I think it is the difference between using an instrument and a
comparator. Yes, the hydrometer is quick and convenient.
Enjoy your weekend.
Best regards,
Ivor Lewis. Redhill, South Australia
Craig Edwards on sat 20 mar 04
Hello Ivor: I enjoy your posts immensely. I not sure if what I'm writing
will be accurate or precise or neither or both. :O) Maybe accurately,
imprecise?
I believe that a viscometer measures the rate at which fluids flow. When
glazes are normally applied they are suspensions, they become fluids
when they melt in the fire.
Harrison devised an instrument that measures the flow of suspensions
called a consistometer (Now there is a cool word, hard to use in normal
conversation). I've seen pictures of this but have never used one.
I'm not sure that the consistometer will give you complete information
as to how a glaze will coat. There are three quantities for determining
how a glaze will coat, coherence value, receptivity, and pickup. Harman
has worked on a dipping plate method that seems to be of value.
Regards,
Craig Edwards
New London MN
>Hydrometers measure Fluid Density. A Viscometer measures the rate at
>which things will flow. Linear intervals measure "...thickness..."
>When you say << ...they want to know whether the glaze is in the range
>of thickness which is suitable for the application technique they are
>using...>> do you mean "...is this going to flow evenly over the pot
>when I dip or when I spray or when I brush..." Or do you mean "... I
>will get the coating thickness I need when I dip the pot into this
>slop for five seconds..."
>Pass/Fail and Go/No Go gauges are very useful tools for quick
>discrimination. Once the standard is established there is no need to
>for higher skills or knowledge.
>The term "Heat Work " is a Tautology". A useful colloquialism never
>the less that we can all understand
><<...Ah, semantics... >> Where would we be without words ???
>Best regards,
>Ivor Lewis. Redhill, South Australia
>
>
>
Ivor and Olive Lewis on sat 20 mar 04
Dear Deg Dewitt,
Hydrometers work because they have a mass to volume ratio which allows
them to float with the scale partially submerged and partly in free
air. Adding more mass without a proportional adjustment in vacant
volumetric space to maintain buoyancy will cause these instruments to
sink.
Accuracy comes from calibration of the rod which holds the scale.
Longer scales give greater precision in a free flowing fluid. In a
slurry, sediment which settles on the shoulder of the glass envelope
will cause a false reading.
I think this is more complex than we realise.
Best regards,
Ivor.
Craig Edwards on sun 21 mar 04
Hello Ivor: The full reference--Harrison, W. N.1927, Controlling the
consistency of enamel slips. Tech. paper no. 356, U.S. Bureau of Standards.
It's a basic flux type instrument. A large tube that acts as a reservoir
into which a stopper with a smaller tube is inserted. The amount of time
that it takes for the slip to flow out of the reservoir through the tube
is timed. It's main application is quality control in a factory. It's
abit of an antique.There are a group of instruments used to measure slip
from the first half of the last century that are real barnyard
oddities. None in itself gives you all the information that you
sometimes need to know.
Coherent value is the weight of slip that remains on an area unit when
it is dipped. Receptivity is ability of the body to accept water. For
example if you have a clay body that is fairly open and bisqued rather
low, it would have a high receptivity index. If your substrate was more
vitreous there would be not as much capillary action and it would have a
low index.
Pickup is the quantity of slip(weight in solids) that is actually
deposited on the body per surface unit.
I worked on a project that we needed to come up with a slip that had
teflon like qualities. It would stick to the substate but not to the
optical glass that was slumped in it. It had to apply very smoothly and
be of precise thickness.
These were a few of the things that came under consideration. I've made
it brief, an outline if you will.
If you would care to explore this more off list I would be glad to-- I'm
afraid that getting any more technical than this would be a real yawn
for most of the list.
Cheers,
Craig Edwards
New London MN
Ivor and Olive Lewis wrote:
>Dear Craig,
>Do you have the full reference for that "Harrison" instrument and the
>definitions of the qualities being assessed?
>Might be a useful tool for a lot of us.
>Best regards,
>Ivor Lewis. Redhill, South Australia
><>called a consistometer >>
><>coherence value, receptivity, and pickup. >>
>
>
>
>
Kathi LeSueur on sun 21 mar 04
craigedwards@CHARTER.NET wrote:
> Hello Ivor: I enjoy your posts immensely. I not sure if what I'm writing
> will be accurate or precise or neither or both. :O) Maybe accurately,
> imprecise?
> I believe that a viscometer measures the rate at which fluids flow. When
> glazes are normally applied they are suspensions, they become fluids
> when they melt in the fire.>>>
Viscosity, specific gravity-- it doesn't matter what you call it. All
most of us want to know is, is the damn stuff thick enough or too thick
to glaze with.
Kathi
Craig Edwards on sun 21 mar 04
Hello Janet: You are totally right on. The name of this list is Clayart,
not Clayscience. I must apogize for going down the techy road. I have
been a consultant on projects for industry that call for precise
thickness on ceramic coatings, as well as other properties. The defining
of parameters and developing tests and measurements are the job. The
gizmos tell us things that no "feel" or "nose" is sensitive, or
experienced enough to discern. For almost everybody on the list these
gizmos are complete frivolous luxuries. Also, for most, the discussion
of them are as interesting as yesterday's dishwater. They are of
absolute no import to the potter.
I looked at my chalk board at my studio this morning. There were La
Place transforms where there should have been sketches of tea bowls.
I've got a spring wood firing coming up like a freight train, how could
I be thinking about transit glaze response. What the hell am I thinking=20
about.
Again Janet, thanks for putting me back on the road of a more artistic
sensibility.
Cheers
~Craig Edwards
New London MN
Janet Kaiser wrote:
>I never take any notice of these little disagreements, but this
>caught my eye. I may be missing something, however...
>
>To be truthful and honest, does it really matter which gadget,
>gizmo, measurement tool or technique anyone uses to replace the
>evidence of hands + eyes + practice + experience? Surely one is
>only doing precisely that, finding "the means to an end". So as
>long as the results of any "test" or "measurement" are totally
>constant and repeatable time after time, thus replacing the
>"feel" or the "nose" of the Old Timer, does it matter how one
>gets there?
>
>And having found a method which suits the individual, who is to
>say there are not "better" methods or techniques more suitable
>for others? Sorry, but I really and truly cannot get excited or
>het up about any sort of methodology, as I am sure others quite
>agree!
>
>Seems to be nit picking for the sake of nothing better to do,
>besides having tools which are a "luxury" rather than a
>necessity. It also somehow reminds me of an ex-colleague who
>started off with a 286 PC about 20 years ago, has upgraded
>software from MS Office to the full Adobe suite of programmes,
>renewed every piece of hardware to the top of the range regularly
>and consciously gone from Win 3.1, 95, 98, 2000 and now XP... In
>other words he has spent thousands of DM & =80uros, could say he
>was/is the best equipped home-user in town, but (and this is the
>rider) he still cannot send an e-mail or print a letter!!! Truly!
>You may know similar examples of fully equipped workshops but the
>owner is unable to hit a nail straight and would not know an awl
>from his all.
>
>Ah, well... Takes all sorts. Keeps us off the streets!
>
>Sincerely
>
>Janet Kaiser -- From the pinch-of-this-and-spoon-of-that school
>of thought, who was repeatedly reprimanded for not doing sums the
>way teacher taught... Always got the right answer though...
>
> =20
>
Ivor and Olive Lewis on sun 21 mar 04
Dear Craig,
Do you have the full reference for that "Harrison" instrument and the
definitions of the qualities being assessed?
Might be a useful tool for a lot of us.
Best regards,
Ivor Lewis. Redhill, South Australia
<called a consistometer >>
<coherence value, receptivity, and pickup. >>
Janet Kaiser on sun 21 mar 04
I never take any notice of these little disagreements, but this
caught my eye. I may be missing something, however...
To be truthful and honest, does it really matter which gadget,
gizmo, measurement tool or technique anyone uses to replace the
evidence of hands + eyes + practice + experience? Surely one is
only doing precisely that, finding "the means to an end". So as
long as the results of any "test" or "measurement" are totally
constant and repeatable time after time, thus replacing the
"feel" or the "nose" of the Old Timer, does it matter how one
gets there?
And having found a method which suits the individual, who is to
say there are not "better" methods or techniques more suitable
for others? Sorry, but I really and truly cannot get excited or
het up about any sort of methodology, as I am sure others quite
agree!
Seems to be nit picking for the sake of nothing better to do,
besides having tools which are a "luxury" rather than a
necessity. It also somehow reminds me of an ex-colleague who
started off with a 286 PC about 20 years ago, has upgraded
software from MS Office to the full Adobe suite of programmes,
renewed every piece of hardware to the top of the range regularly
and consciously gone from Win 3.1, 95, 98, 2000 and now XP... In
other words he has spent thousands of DM & =80uros, could say he
was/is the best equipped home-user in town, but (and this is the
rider) he still cannot send an e-mail or print a letter!!! Truly!
You may know similar examples of fully equipped workshops but the
owner is unable to hit a nail straight and would not know an awl
from his all.
Ah, well... Takes all sorts. Keeps us off the streets!
Sincerely
Janet Kaiser -- From the pinch-of-this-and-spoon-of-that school
of thought, who was repeatedly reprimanded for not doing sums the
way teacher taught... Always got the right answer though...
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The Chapel of Art : Capel Celfyddyd
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Home of The International Potters' Path
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Ivor and Olive Lewis on sun 21 mar 04
Dear Ingeborg,
Excellent point and valid criticism.
The tenor of the discussion is changing from using Hydrometers to that
of reliability of other forms of instrumentation.
This is not a can of worms, but a vipers nest if people are not
willing to explore the use of the terms involved and then apply them
with consistency. I did introduced two to clarify a point, "Precision"
and "Accuracy". I would add another essential ingredient, "Error".
Since modern technology is taking our Art away from the realms of
craftsmanship where "Eye and Hand" are adequate test instruments, then
those in the authoritative position of Teacher should ensure they
include segments about Mensuration of all of the parameters needed to
accomplish work in hand.
Best regards,
Ivor Lewis. Redhill, South Australia
Ivor and Olive Lewis on mon 22 mar 04
Dear Kathi,
You say <<...All most of us want to know is, is the damn stuff thick
enough or too thick
to glaze with... >>
Which is why I suggested a bisque rod as a substitute for a naked
finger.
But it is important that we discriminate between Viscosity and
Specific Gravity for the benefit of future students.
Imagine you have coins in your pocket. They are just metal coins and
one will substitute for another if you wish to scribe a circle. But,
for their actual function it matters a lot. Some may be Copper and
some are Gold. Which would you prefer to possess? My belief is that
the same consideration should be given to Words.
Best regards,
Ivor Lewis. Redhill, South Australia
Ivor and Olive Lewis on mon 22 mar 04
Dear Craig,
I think I get the picture.
This sounds very much like an original form of Viscometer. Almost the
same as that provided to me by paint people for finding if the paint
is the right consistency to spray or brush.
Receptivity is an interesting thought. Related to the ratio of
theoretical density and actual density. I think my roll of bisque
dipped into the glaze covers this as well as the notion of "Pick Up"
As you say to go any deeper with the topic is needless. In a Studio
rules of thumb stand the test of time well. In an industrial mass
production setting instrumentation at this level is necessary to
ensure product uniformity. But it seems to me as though artists look
for variation.
Thanks for your information.
Best regards,
Ivor Lewis. Redhill, South Australia
----- Original Message -----
From: "Craig Edwards"
To:
Sent: Monday, 22 March 2004 8:06
Subject: Re: Hydrometers... the case for the defence (again)
> Hello Ivor: The full reference--Harrison, W. N.1927, Controlling the
> consistency of enamel slips. Tech. paper no. 356, U.S. Bureau of
Standards.
> It's a basic flux type instrument. A large tube that acts as a
reservoir
> into which a stopper with a smaller tube is inserted. The amount of
time
> that it takes for the slip to flow out of the reservoir through the
tube
> is timed. It's main application is quality control in a factory.
It's
> abit of an antique.There are a group of instruments used to measure
slip
> from the first half of the last century that are real barnyard
> oddities. None in itself gives you all the information that you
> sometimes need to know.
> Coherent value is the weight of slip that remains on an area unit
when
> it is dipped. Receptivity is ability of the body to accept water.
For
> example if you have a clay body that is fairly open and bisqued
rather
> low, it would have a high receptivity index. If your substrate was
more
> vitreous there would be not as much capillary action and it would
have a
> low index.
> Pickup is the quantity of slip(weight in solids) that is actually
> deposited on the body per surface unit.
> I worked on a project that we needed to come up with a slip that had
> teflon like qualities. It would stick to the substate but not to the
> optical glass that was slumped in it. It had to apply very smoothly
and
> be of precise thickness.
> These were a few of the things that came under consideration. I've
made
> it brief, an outline if you will.
> If you would care to explore this more off list I would be glad to--
I'm
> afraid that getting any more technical than this would be a real
yawn
> for most of the list.
> Cheers,
> Craig Edwards
> New London MN
>
>
>
>
> Ivor and Olive Lewis wrote:
>
> >Dear Craig,
> >Do you have the full reference for that "Harrison" instrument and
the
> >definitions of the qualities being assessed?
> >Might be a useful tool for a lot of us.
> >Best regards,
> >Ivor Lewis. Redhill, South Australia
> ><suspensions
> >called a consistometer >>
> ><> >coherence value, receptivity, and pickup. >>
> >
> >
> >
> >
>
>
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Craig Edwards on tue 23 mar 04
Hello Ivor: Your use of the bisque rod for the studio setting is
brilliant. It deals simply with both the glaze and the body. SP gives
you numbers for the glaze, but doesn't take into account for
receptively of the body. Lacking a bisque rod, a bisque waster would
probably work for the "potter on the go" lifestyle of some. Dip,dry and
then scratch the coating with your fingernail that hasn't been worn down
from throwing, to give you the numbers on the thickness( the thick side
of thin). Into the kiln on Tuesday, out to the show on Saturday. Repeat
as necessary. Sounds vaguely familiar.;O)
Cheers
Craig Edwards
New London MN
Ivor and Olive Lewis wrote:
>Dear Kathi,
>You say <<...All most of us want to know is, is the damn stuff thick
>enough or too thick
>to glaze with... >>
>Which is why I suggested a bisque rod as a substitute for a naked
>finger.
>
>
>
Craig Edwards on tue 23 mar 04
Hello Ivor: I think that you got it. Here is another approach think you
might find amusing. It was called the mobilometer, it measures the rate
at which an object would fall through a slip. A novel approach. The
science of how colloidal suspensions work, took on meaning in the first
part of the last century. In the 1910 era when the viscosity of a glaze
was mentioned, they were referring to application. By 1925 the viscosity
of a glaze was how it moved in the melt. The different instruments that
were devised to measure how suspensions worked are an interesting study
on the evolution of a science. Let me qualify that, interesting only if
your interested in it. :O)
Let me bore you with a short story. In the late 70's I was stirring a
glaze. When it was just stirred it was fluid but soon would set to a
pudding consistency. From studies and etc. I could explain why--
regurgitate knowledge, if you will. I realized that I could explain, but
I didn't understand how suspensions really worked. It sparked a
consuming need to know what was really going on in that bucket, it
became an obsession. As they say now 24/7. I can't remember all the
thoughts, but one that sticks out was how eloquent the water molecule
was. The deeper understanding translated into a viable application/
process that was of use to the ceramic industry. Their gratitude
translated into a much nicer studio for me.
The Best,
Craig Edwards
New London, MN
Ivor and Olive Lewis wrote:
>Dear Craig,
>I think I get the picture.
>This sounds very much like an original form of Viscometer. Almost the
>same as that provided to me by paint people for finding if the paint
>is the right consistency to spray or brush.
>
>
>
Ivor and Olive Lewis on wed 24 mar 04
Dear Craig,
My standard test piece is a flat tile, 6*2 1/4 thick. While the clay
is still soft part of it is textured along one edge. Glaze is always
applied in three thicknesses.
It is a style of working I acquired from Greg Daly.
Now I shall have to start using that sausage dip test on my new
glazes.
Best regards and thanks for the accolade.
Ivor Lewis. Redhill, South Australia
Janet Kaiser on wed 24 mar 04
Craig, dear! (And whoever else was enjoying the "to hydromate it
or not to mate it debate"... )
Let me just say one thing... "Whatever turns you on"! Truly! It
is good to see people enjoying themselves, so no need to
apologise! No... I just do not get what all the fuss is about and
that poor gal who asked about glazing... Yikes!! Almost as bad as
asking how to calculate the circumference of a circle and being
lectured on the Law of Relativity! Ha! Ha!!! (That actually
happened to me... I think Ivor has a long-lost twin he does not
know about alive and well in Wales! :o)
But to know I got you back on the straight and narrow, Craig...
Well, I will regard that as my good deed for the day or maybe
even the week! You just forget all that techy stuff until you
really have the time and the leisure... If I was having to do all
you list myself... Well, I would suspect I recognise the
technique of dealing with panic..!?!? Do anything and everything
which does not need doing, so it does not appear as
procrastination to casual observers!? I can almost feel that
overwhelming feeling that rises up from the stomach to the chest
when I do not know where and how to start to get all that I have
to do begun, let alone completed on target... Indeed, I still
suffer nightmares about my finals... Especially at times of
stress!
As for the glaze thickness... Did anyone actually spell out the
facts of life when it comes to glazes? Do we know what level to
pitch the information at and what experience the questioner has?
I do not know if anyone has ever "consolidated" a mail (as the
other Mr. Edwards would say) about glazing, including
thickness... I cannot believe there is a wealth of information
already archived, but like I say, I do not take much notice of
glazing questions. Sorry!!
Sincerely
Janet Kaiser -- sore after being in a Dr. Edward's chair this
afternoon. Off to another Dr. Edwards for assessment on
Thursday... Busy, busy... But still not quite ready to "reveal
all"... A clue... Our own Clayart Glaze Queen is involved... But
ssssshhhhh Do not say anything... :o)
*** IN REPLY TO THE FOLLOWING MAIL:
>Hello Janet: You are totally right on. The name of this list is
Clayart,
>not Clayscience. I must apogize for going down the techy road.
>snip<
>I looked at my chalk board at my studio this morning. There were
La
>Place transforms where there should have been sketches of tea
bowls.
>I've got a spring wood firing coming up like a freight train,
how could
>I be thinking about transit glaze response. What the hell am I
thinking
>about. Again Janet, thanks for putting me back on the road of a
more artistic
>sensibility.
*** THE MAIL FROM Craig Edwards ENDS HERE ***
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8 Marine Crescent : Criccieth : Wales : UK
Home of The International Potters' Path
Tel: ++44 (01766) 523570 http://www.the-coa.org.uk
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John Hesselberth on thu 25 mar 04
On Thursday, March 25, 2004, at 03:45 PM, Roger Graham wrote:
> No doubt there are situations where hydrometers DON'T give a reliable
> result. Measuring dense casting slip must surely be one such. But for
> glazes... well, don't just argue about it. Make some real measurements
> on
> glazes, and post the results. I might still be wrong (again). But
> convince
> me.
Hi Roger,
And that is just the problem. With some glazes it will be OK; with
others it will not. Which are which? I have done the experiments (with
glazes) in the past and don't plan to do them again to try to convince
you or anyone else. Weighing a constant volume is accurate all the
time; using a hydrometer is accurate some of the time. As Vince pointed
out it is fine with terra sig. The thicker you mix your glazes the more
likely it is to be inaccurate or imprecise. You do it your way; I will
continue to do it mine and advise others of the potential problem with
hydrometers.
Regards,
John
http://www.frogpondpottery.com
http://www.masteringglazes.com
Ivor and Olive Lewis on fri 26 mar 04
Dear Roger Graham,
That's what I like to read.
Pragmatic and Empirical.
Nothing like getting back to basics.
Best regards,
Ivor Lewis. Redhill, South Australia
Roger wrote
<<, the hydrometers involved all began life as McDonalds drinking
straws, a universally available starting point. About 207 mm long,
7mm diameter, weighing just under a gram. Find a small dense object of
weight about 4 grams, smear it with silicone sealant,
> and poke it into the end of the straw. Completely in, no knobby bits
sticking out. Straw should now float upright in water with about 120
mm submerged, and you make the mark 1.0 on the straw at the waterline.
There.. you've just made a hydrometer. Not moon rocket science at all.
Calibration most easily done with a chart, still available on Des
Howard's web pages (www.luepottery.hwy.com.au/clayart.htm) Don't
just
> argue about it. Try it.
>
> Roger Graham, near Gerringong, Australia
Roger Graham on fri 26 mar 04
Can you die of an overdose of hydrometer arguments? Could be. All this
repetition gets tedious. Yawn. But do make room for just one more.
I still believe that a simple hydrometer can give reliable numerical values
for the specific gravity of glazes. Motivated by
the snorts of disbelief that greeted this heresy last week, I searched in
the workshop to see if there were any hydrometers left from the last
batch made to give away. Found seven, brand new, unused, stored away in a
box. The idea was, try them all side by side in the same glaze and see
if their results were consistent. And of course, compare the readings
with a more accurate measurement by the "relative density bottle" method.
This time, instead of choosing a normal stoneware glaze, I looked for
something more viscous and slimy. Found a bottle of terra sigillata, stored
away years ago, creamy and thick. Shook well, stirred, poured into a tall
preserving jar, deep enough to float a hydrometer. Tried all seven
hydrometers one by one, and wrote down the SG readings.
For those paranoid about viscosity and shear forces, just whacked the side
of the jar to agitate the fluid a bit. Kept tapping until the hydrometer
didn't sink any further. Maybe six or seven times.
Did it all again, dipping each straw in water first as Michael McDowell
suggests. Sure enough, the straws slid more easily through the viscous
creamy
fluid, but the final levels were unchanged. Just didn't have to whack the
bottle so much.
Did it all again, that made three measurements for each hydrometer. And no,
the three readings for each straw weren't necessarily identical. Sometimes
yes, sometimes no. For example 1.19, then 1.18, then 1.18 But never more
than a few percentage points different.
Worked out the average for each hydrometer. Four came out 1.18, one at 1.19,
two at 1.20 This is the place to say that the seven hydrometers weren't
calibrated with any pretensions about precision. Just the usual dab with a
felt-tipped pen, against calibration lines on the chart.
Now finally, measured the SG of the white creamy stuff by weighing in a
stubby beer bottle of volume 391 millilitres. Answer, 460 grams, so the
specific gravity is 460/391 which, to two decimal places, is 1.18 No reason
here to vilify the poor inoffensive hydrometers. Less than 2
percent out, worst case.
I think what's needed now is less prejudice and more experimental results .
No doubt there are situations where hydrometers DON'T give a reliable
result. Measuring dense casting slip must surely be one such. But for
glazes... well, don't just argue about it. Make some real measurements on
glazes, and post the results. I might still be wrong (again). But convince
me.
For those who haven't been following, the hydrometers involved all began
life as McDonalds drinking straws, a universally available starting
point. About 207 mm long, 7mm diameter, weighing just under a gram. Find a
small dense object of weight about 4 grams, smear it with silicone sealant,
and poke it into the end of the straw. Completely in, no knobby bits
sticking out. Straw should now float upright in water with
about 120 mm submerged, and you make the mark 1.0 on the straw at the
waterline. There.. you've just made a hydrometer. Not moon rocket science
at all. Calibration most easily done with a chart, still available on Des
Howard's web pages (www.luepottery.hwy.com.au/clayart.htm) Don't just
argue about it. Try it.
Roger Graham, near Gerringong, Australia
http://members.optusnet.com.au/~rogergraham
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