Elizabeth Fusaro on wed 10 apr 96
After almost 20 years of making pots in one area, we moved
to Tallahassee, FL , where the humidity is like the rain
forests of Costa Rica. Many of my old standard glazes now
behave differently.
Got a hydrometer from a ceramics supply company, but it
had no instructions. Can someone tell me how to accurately
use it in glazes and decorating slips?
Thanks.
Beth Fusaro
Sun & Moon Pottery
Tallahassee, FL
BobWicks@aol.com on thu 11 apr 96
Beth:
I have used hydrometers to measure the specific gravity of my glazes and
slips. First it will do well to find the glaze consistency that you feel is
best for you. I'm sure some one will try to tell the exact S.G (Specific
Gravity). but you should try to customize it to your likes. After finding
the ideal consistency, take a measurement with the hydrometer and record it
in your log. The next time you want to duiplicate it, just measure the S.G.
and make adjustments to your mixture until you get the same reading. I have
made hydrometers using a wood dowel and wind a copper wire ball about 2/3
from the end and insert it in the glaze. Your reading can be marked on the
stick where the glaze reaches.
S.G. Gravity tells you the ratio of the densityof a substance to the density
of a substance (as pure water) taken as a standard when both densities are
weighed in air. By adjusting the contents of your glaze in relationship to
the water and or electrolyte you can change the S.G.
If you have questions or I have left something unclear sen me an E mail.
Bobwicks@aol.com
Ellen L Price on thu 11 apr 96
In my production pottery studio, I used a hydrometer for beer
making. I marked a line on it with a red china marker when I achieved
the glaze consistency I wanted.
Ellen In the desert.
On Thu, 11 Apr 1996 BobWicks@aol.com wrote:
> ----------------------------Original message----------------------------
> Beth:
> I have used hydrometers to measure the specific gravity of my glazes and
> slips. First it will do well to find the glaze consistency that you feel is
> best for you. I'm sure some one will try to tell the exact S.G (Specific
> Gravity). but you should try to customize it to your likes. After finding
> the ideal consistency, take a measurement with the hydrometer and record it
> in your log. The next time you want to duiplicate it, just measure the S.G.
> and make adjustments to your mixture until you get the same reading. I have
> made hydrometers using a wood dowel and wind a copper wire ball about 2/3
> from the end and insert it in the glaze. Your reading can be marked on the
> stick where the glaze reaches.
> S.G. Gravity tells you the ratio of the densityof a substance to the density
> of a substance (as pure water) taken as a standard when both densities are
> weighed in air. By adjusting the contents of your glaze in relationship to
> the water and or electrolyte you can change the S.G.
>
> If you have questions or I have left something unclear sen me an E mail.
>
> Bobwicks@aol.com
>
Don Kopyscinski on fri 12 apr 96
Hi Everyone,
Recently Bob Wicks wrote:
>S.G. Gravity tells you the ratio of the densityof a substance to the density
of a substance (as pure water) taken as a standard when both densities are
weighed in air. By adjusting the contents of your glaze in relationship to
the water and or electrolyte you can change the S.G.<
I couldn't resist this, and for those that have already read the long version of
this many times over (it's my pet crusade) I'll keep it short.
It's this part that bugs me:
>By adjusting the contents of your glaze in relationship to the water and or
electrolyte you can change the S.G.<
The addition of electrolyte isn't really changing the S.G., it's only fooling
the hydrometer into giving a false reading. True S.G. in a suspension can only
be had by weighing a given volume (most conveniently 100ML) and comparing it to
the weight of the same volume of water (using a 100ML gradudated cylinder and
divide weight of the glaze in grams by 100 to get S.G.). The fluidity of the
glaze can then be measured using a flow tube etc... (see Parmalee "Ceramic
Glazes"). Flocculation and Deflocculation cause changes in viscosity (fluidity
of raw glaze) of a glaze given S.G., but have no effect on S.G.
Regards,
Don Kopyscinski
Bear Hills Pottery
ROBERT POGSON on sat 13 apr 96
DK> It's this part that bugs me:
DK> >By adjusting the contents of your glaze in relationship to the water and o
DK> electrolyte you can change the S.G.<
DK>
DK> The addition of electrolyte isn't really changing the S.G., it's only fooli
DK> the hydrometer into giving a false reading. True S.G. in a suspension can o
DK> be had by weighing a given volume (most conveniently 100ML) and comparing i
DK> the weight of the same volume of water (using a 100ML gradudated cylinder a
DK> divide weight of the glaze in grams by 100 to get S.G.). The fluidity of
DK> glaze can then be measured using a flow tube etc... (see Parmalee "Ceramic
DK> Glazes"). Flocculation and Deflocculation cause changes in viscosity (fluid
DK> of raw glaze) of a glaze given S.G., but have no effect on S.G.
DK>
DK> Regards,
DK> Don Kopyscinski
DK> Bear Hills Pottery
DK>
Two things I can say about that:
1)If I add dry clay to water and stir, I get to a point where the mix
coagulates. If I measure the density, I can tell I need deflocculation
because the density is not high enough. I then add electrolyte. Fluidity
returns and I add more dry. This process converges to the density specified
for a particular slip or glaze. Therefor one can say loosely that electrolyte
changes the specific gravity of the slip. The electrolyte must be reducing
the density because adding electrolyte permits one to add more clay.
2)Deflocculation involves altering the tendency of the clay particles from
adhering by introducing ionized particles that adhere to the clay and prevent
clay to clay bonding. I would expect deflocculation to reduce the density
of the slip because the clay particles are now more widely dispersed. This
effect will be small because we are not doing this molecule by molecule but
on larger particles, but the effect will be there.
.... nfx v2.8 [C0000] Mice: toys for cats
Don Kopyscinski on sun 14 apr 96
Hi Robert,
You wrote:
robert.pogson@mwcs.mb.ca>
Subject: Re: hydrometers
snip>>The electrolyte must be reducing the density because adding electrolyte
permits one to add more clay.<<
The point I'm trying to make is that the hydrometer will not give an accurate
reading when used to read density expressed as SG. If you were to take a
hydrometer reading before you added the electrolyte to that gel, you would get a
high reading. Upon deflocculation (by additions of a small percentage of an
electrolyte) the reading would be *dramatically altered* and not a true
representation in any real change in density that has happened in the system. A
pint weight method is much more reliable because it isn't inferring SG from the
behavior of a floating object whose buoyancy may be manipulated.
snip>> I would expect deflocculation to reduce the density of the slip because
the clay particles are now more widely dispersed.<<
I wondered about this. I think it's a function of reduced friction caused by
minute electrical attraction of the particles. I'm not sure if it is accompanied
by any change in volume or true density as expressed in SG. Again, I think that
the effect such changes has on a hydrometer reading isn't representative of any
real change in density.
I searched several texts looking for the difinative answer. After reading
several articles on ionic exchange, and trying to grasp the complexities of,
base exchange, electrophoresis, double layer theory, exchangable cations,
thixotropic cefficients, lyophilic suspensions, electro-viscous effect, sol-gel
formation, water imbibition, and colloidal reactions in general.........I can
safely say, there is a lot about the mechanics of the system that I don't
understand.
See:
"Study of factors involved in glaze slip control." Journal of the American
Ceramic Society V. 27, 202-220 (1944).
"Ceramics a Symposium" A.T. Green - The Jubilee Volume of the British Ceramic
Society P. 60-91 (1953)
"Ceramic Glazes" Parmalee P. 119-133 (1951 - revised 1973)
I do know the following:
As a method in determining a baseline for the application qualities of a given
glaze, the hydrometer is effective within limits. The reason this method has
caused several potters problems is that the glaze water suspension isn't a
static one. As solutes act on the glaze it's flow characteristics (and resultant
changes in receptivive values of the glaze) may by dramatically changed (while
the SG remains relatively the same) their hydrometers have led them astray. Most
notably a case where a glaze containing gerstley borate was mixed with very hot
water causing the whole mass to gel over time. The hydrometer reading indicated
a progressive increase in desity of the glaze. The potter kept adding more and
more water to get the desired SG reading. This went on for some time until the
glaze simply jumped off the pots. This was due to saturation of the bisque due
to the increased water in the glaze, the reduced tenacity of the overflocculated
glaze coat, as well as changes in glaze coat thickess. These were all had with
the same hydrometer reading on a dramatically altered glaze. The hydrometer had
been tricked and the potter blindly trusting it, had been too. If a pint weight
method had been employed the excessive flocculation would have been evident
early on, while using the hydrometer alone, it was not.
So.... a floating stick with a mark on it has worked well for many over the
years and may be all someone needs. I just want people to know that there are
other forces at work that may skew the readings. When (and if) problems arise,
it doesn't give you the whole picture.
Regards,
Don Kopyscinski
Bear Hills Pottery
Newtown, CT
74134.2672@Compuserve.com
DonKopy@AOL.com
Tom Buck on mon 15 apr 96
Don K makes an important point about density and hydrometers. The
hydrometer was invented to measure the density of SOLUTIONS not glaze
dispersions (aka slurries). The original use of the hydrometer was as a
saccharometer to measure the sugar content of grape juice; the basis of
the device was that the juice was essentially a solution of grape sugars
in water with small amounts of other soluble materials (eg, food acids,
tannins). Since the juice was a true solution within the narrow range of
interest to winemakers, the hydrometer gave a true indication of the
concentration of the sugars in terms of solution density. Winemakers even
have a term for sugar concentration, degrees BRIX, and placed marks on
their saccharometers accordingly. The meter was extended to measure the
density of other true solutions within the range of a floating device.
One can of course seek to make use of the hydrometer in clay work
but one must also recognize in so doing that the meter will not correctly
reproduce correctly the density of slurries if agglomeration of particles
causes the dispersion to be non-uniform. And that is what happens when
flocculants/deflocculants are used in clay slips ... the basis on which
the hydrometer measures density (archaic term specific gravity) no longer
is true/applies, so the hydrometer will give false readings, useless
readings, and lead the potter astray.
If you have mixed a glaze then deflocculated it, do not depend on
the hydrometer for a valid measurement... it will measure something but it
sure isn't density (or SG). The only reliable way to determine the
density of the slurry (dispersion) then is to measure out a specific
volume (eg, a liter or part thereof) and weigh this volume. Since I have
a small measuring cup that holds 200 milliliters, I use this and weigh
this amount. If I get 300 grams (tare excluded), then my glaze slurry
density is 1.5 g/mL and I know this is ok for spraying but a bit thin for
dipping and way too thin for brushing. I make adjustments accordingly.
Finally, if you use coloured slips as I do, then getting the slip
density right is important for best brush application to wetware. And
weighing it safeguards myapplications. Cheers Tom.Buck, Hamilton Ontario
Canada
ROBERT POGSON on mon 15 apr 96
"the same hydrometer reading on a dramatically altered glaze. The hydrometer
been tricked and the potter blindly trusting it, had been too. If a pint we
method had been employed the excessive flocculation would have been evident
early on, while using the hydrometer alone, it was not.
So.... a floating stick with a mark on it has worked well for many over the
years and may be all someone needs. I just want people to know that there a
other forces at work that may skew the readings. When (and if) problems ari
it doesn't give you the whole picture.
Regards,
Don Kopyscinski
Bear Hills Pottery
Newtown, CT"
The floating stick is simply balancing its weight against the weight of
the slip it displaces. This is exactly what a pycnometer does. The principle
errors in use of a hydrometer are to use too slight an instrument so that
the surface tension effect is significant or to use it without waiting for
it to come to equilibrium.
.... nfx v2.8 [C0000] !noitacidem deen uoy ,egassem siht daer nac uoy fI
Bob Stryker on tue 16 apr 96
I was really trying to stay out of this, but when I read:
"We can debate the principles for as long as we care to, but I'm
willing to bet that those guys at the commercial potty plant would laugh if
we showed up with a hydrometer to check SG."
Well that's absolutely correct in my experience. In the potty(!) plant I
where I used to work, glazes were evaluated using a specific gravity cup for
s.g. and using a Brookfield viscometer to measure viscosity. Often, on a
spray line, an operator would recheck the viscosity using a zahn cup and
stopwatch.
I may be a bit particular (peculiar even) in this area, but I always check
my application thickness (that's the end goal we're shooting for after all
in testing the S.G.) using an eye piece called a pocket comparitor. This is
a tool that can be purchased from Edmund Scientific in New Jersey. It looks
like a jeweler's eye piece but has scale with .001" increments up to .016".
I dip or spray a waster and when it's dry, I break the piece and measure the
cross-section of glaze using the comparitor. Most of my glazes get about
..014" application thickness give or take .002".
I think that using a hydrometer is alright in a studio situation. But as
soon as I suspected an unusual hydrometer reading, I would surely
double-check the situation using a S.G. cup.
Bob Stryker
Minnesota Clay USA
http://www.mm.com/mnclayus/
Elizabeth Hewitt on mon 24 aug 98
Time to get serious about glaze making. I bought a hydrometer, scale and a bunch
other goodies.Before I bought the hydrometer I had read about them in one of my
books......you guessed it, now
that I have the tool, I can't find where that was. I've looked in all of them
checked the
archives of this list, no directions came with it.
If anyone uses one, could you tell me how it's used or lead me to a source of
information that
will tell me.
Thanks for any help you can give me.
Elizabeth
Clyde Tullis on mon 24 aug 98
When you are satisfied with the consistancy of your glaze. Record the reading wi
the formula and the adjust your glaze accordingly in the future. More water if
floats high less if low.
Now that you have bought the tool, I have a different way to make the test. A
small necked plastic bottle, about 4 oz., filled right to the top with glaze. th
wieght sould be the same from time to time. If it is heavy add water if it is
light subtract.
Good luck, Clyde
Elizabeth Hewitt wrote:
> ----------------------------Original message----------------------------
> Time to get serious about glaze making. I bought a hydrometer, scale and a bun
> other goodies.Before I bought the hydrometer I had read about them in one of m
> books......you guessed it, now
> that I have the tool, I can't find where that was. I've looked in all of th
> checked the
> archives of this list, no directions came with it.
>
> If anyone uses one, could you tell me how it's used or lead me to a source of
> information that
> will tell me.
>
> Thanks for any help you can give me.
> Elizabeth
Lynne Berman on sat 5 sep 98
Vince, or other terra sig experts,
Buying a hydrometer doesn't seem to be that easy. Some work only on slip,
others only on glaze. Some don't have the 1.12 to 1.18 kind of range, others
come without directions. Any suggestions?
Lynne in Philadelphia
kurt l wild on sun 6 sep 98
Lynne Berman wrote:
> ----------------------------Original message----------------------------
> Vince, or other terra sig experts,
>
> Buying a hydrometer doesn't seem to be that easy. Some work only on slip,
> others only on glaze. Some don't have the 1.12 to 1.18 kind of range, others
> come without directions. Any suggestions?
>
> Lynne in Philadelphia
The best suggestion I have is to check out what is available at your nearest
auto parts store instead of a clay supply house. My hydrometer was purchased at
an auto parts store and reads from 1300 (1.3) to 1100 (1,1). Mine is rather old
so maybe such a type is not readily available. It has a rather large tube
(about 1" in diam) and has I nice large bulb on the upper end.
--
Kurt Wild
1000 E. Cascade
River falls, WI 54022 Phone: (715) 425-5715
web site: http://www.uwrf.edu/art/faculty/Wild
kurt l wild on sun 6 sep 98
Lynne Berman wrote:
> ----------------------------Original message----------------------------
> Vince, or other terra sig experts,
>
> Buying a hydrometer doesn't seem to be that easy. Some work only on slip,
> others only on glaze. Some don't have the 1.12 to 1.18 kind of range, others
> come without directions. Any suggestions?
>
> Lynne in Philadelphia
The best suggestion I have is to check out what is available at your nearest
auto parts store instead of a clay supply house. My hydrometer was purchased at
an auto parts store and reads from 1300 (1.3) to 1100 (1,1). Mine is rather old
so maybe such a type is not readily available. It has a rather large tube
(about 1" in diam) and has I nice large bulb on the upper end.
--
Kurt Wild
1000 E. Cascade
River falls, WI 54022 Phone: (715) 425-5715
web site: http://www.uwrf.edu/art/faculty/Wild
Graham Jones on mon 7 sep 98
You can also buy hydrometers at home brew supply shops. They come in one
range for beer and another for wine.
My beer one goes from 1000 to 1100
And the wine 990 to 1120
They will allso give you the potential alcohol % by volume.(:-)
Graham Jones
Sydney Australia
Where we can't drink the tap water so have to drink beer.
-----Original Message-----
From: kurt l wild
To: CLAYART@LSV.UKY.EDU
Date: Monday, September 07, 1998 12:13 PM
Subject: Re: Hydrometers
>----------------------------Original message----------------------------
>
>
>Lynne Berman wrote:
>
>> ----------------------------Original message----------------------------
>> Vince, or other terra sig experts,
>>
>> Buying a hydrometer doesn't seem to be that easy. Some work only on slip,
>> others only on glaze. Some don't have the 1.12 to 1.18 kind of range,
others
>> come without directions. Any suggestions?
>>
>> Lynne in Philadelphia
>
> The best suggestion I have is to check out what is available at your
nearest
>auto parts store instead of a clay supply house. My hydrometer was
purchased at
>an auto parts store and reads from 1300 (1.3) to 1100 (1,1). Mine is
rather old
>so maybe such a type is not readily available. It has a rather large tube
>(about 1" in diam) and has I nice large bulb on the upper end.
>
>--
>Kurt Wild
>1000 E. Cascade
>River falls, WI 54022 Phone: (715) 425-5715
>
>web site: http://www.uwrf.edu/art/faculty/Wild
>
Stephen Mills on mon 7 sep 98
Hydrometers tend to be rather frail. I made my own using a heavy
duty test tube. I zero'd it by floating it in water and putting
in small amounts of shotgun shot 'till the top was level with
the surface, then setting the shot in place with wax. The scale
was home made and held in place with super-glue (cynoacrilate)
and the whole thing topped off with a cork. 20+ years later I
still have it!
Steve
Bath
UK
In message , kurt l wild writes
>----------------------------Original message----------------------------
>
>
>Lynne Berman wrote:
>
>> ----------------------------Original message----------------------------
>> Vince, or other terra sig experts,
>>
>> Buying a hydrometer doesn't seem to be that easy. Some work only on slip,
>> others only on glaze. Some don't have the 1.12 to 1.18 kind of range, others
>> come without directions. Any suggestions?
>>
>> Lynne in Philadelphia
>
> The best suggestion I have is to check out what is available at your nearest
>auto parts store instead of a clay supply house. My hydrometer was purchased a
>an auto parts store and reads from 1300 (1.3) to 1100 (1,1). Mine is rather ol
>so maybe such a type is not readily available. It has a rather large tube
>(about 1" in diam) and has I nice large bulb on the upper end.
>
>--
>Kurt Wild
>1000 E. Cascade
>River falls, WI 54022 Phone: (715) 425-5715
>
>web site: http://www.uwrf.edu/art/faculty/Wild
>
--
Steve Mills
Bath
UK
home e-mail: stevemills@mudslinger.demon.co.uk
work e-mail: stevemills@bathpotters.demon.co.uk
own website: http://www.mudslinger.demon.co.uk
BPS website: http://www.bathpotters.demon.co.uk
Gregory D Lamont on tue 8 sep 98
Hi Lynne,
You could always find the specific gravity the "old fashioned" way:
1) Zero out your gram scale and use the poise tare bar to balance out a
clear container.
2) Fill this containter with 100 grams of water
3) Carefully mark the level of the water on the container with an
indelible fine-point marker. ( Accuracy is important here).
4) Empty out the water and fill container to the mark with terra sig,
glaze or slip. (Accuracy is important here, too).
5) Balance out scale to the new weight. If the scale reads 120 grams
the ratio is 1.2, etc.
This method is the one Pete Pinnell taught me to use as it is always very
accurate and foolproof! Some hydrometers are meant to measure solutions
and not suspensions--which is what glazes, slips, etc. are.
Greg
At 12:29 PM 9/5/98 EDT, you wrote:
>----------------------------Original message----------------------------
>Vince, or other terra sig experts,
>
>Buying a hydrometer doesn't seem to be that easy. Some work only on slip,
>others only on glaze. Some don't have the 1.12 to 1.18 kind of range, others
>come without directions. Any suggestions?
>
>Lynne in Philadelphia
>
Greg Lamont
3011 Northwood Dr.
Ames, Iowa 50010-4750
515.233.3442
gdlamont@iastate.edu
Timothy Dean Malm on tue 8 sep 98
If a hydrometer is on your tool list, find the kocal beer making supply
house. It is a tool to find the specific gravity of beer fermentation.Tim
Malm
Vince Pitelka on tue 8 sep 98
Six months ago or so I posted a message about a hydrometer I found in the
VWR Scientific Products catalog (800/932-5000 - www.vwrsp.com), which
according to the description seemed especially appropriate for use with
terra sig (and thin slips and glazes). I have not ordered this hydrometer,
but all the specs are right. It is designed for testing small volumes of
heavy liquids, is 6.5" (165mm) long, has a s.g. scale from 1.00 to 2.00, and
costs $19.97 each - catalog number is #34640-207.
The reason I have not ordered one of these VWR hydrometers is as follows. I
ordered my first glaze hydrometer from Ceramics and Crafts in San Francisco
about 20 years ago. The first time I used it I shook it off, and snapped it
in half. Of course, in order for a hydrometer to float upright, the upper
half must be very light-weight, and in this hydrometer the glass was
paper-thin. So I immediately ordered two more of the same, and treated them
carefully during subsequent use. 20 years later, I still have both.
- Vince
Vince Pitelka - vpitelka@DeKalb.net
Home 615/597-5376, work 615/597-6801, fax 615/597-6803
Appalachian Center for Crafts
Tennessee Technological University
1560 Craft Center Drive, Smithville TN 37166
Vince Pitelka on tue 8 sep 98
>You can also buy hydrometers at home brew supply shops. They come in one
>range for beer and another for wine.
>
>My beer one goes from 1000 to 1100
>And the wine 990 to 1120
Be careful of this. As wine and beer develop alcohol content, they become
lighter than water, or at least at the very light end of the hydrometer
scale, and thus most wine-maker's hydrometers do not go high enough for
measuring specific gravity of slips and glazes.
- Vince
Vince Pitelka - vpitelka@DeKalb.net
Home 615/597-5376, work 615/597-6801, fax 615/597-6803
Appalachian Center for Crafts
Tennessee Technological University
1560 Craft Center Drive, Smithville TN 37166
John Hesselberth on thu 10 sep 98
>----------------------------Original message----------------------------
You could always find the specific gravity the "old fashioned" way:
1) Zero out your gram scale and use the poise tare bar to balance out
a
clear container.
2) Fill this containter with 100 grams of water
3) Carefully mark the level of the water on the container with an
indelible fine-point marker. ( Accuracy is important
here).
.........
________________________________
Here's an even simpler way. Same principle as above:
Take any container. Weigh it empty (or set the tare weight on your scale
to zero it out). Weigh it full of water. Weigh it full of glaze or slip.
Specific gravity = (weight w glaze or slip - weight empty) / (weight w
water - weight empty)
Just about as quick as a hydrometer and almost always more accurate as
hydrometers don't always settle to the same place in a thick glaze or
slip. I wouldn't use a hydrometer for specific gravity of suspensions.
They work OK for homogeneous liquids.
John Hesselberth
Frog Pond Pottery
Pocopson, PA 19366 USA
EMail: john@frogpondpottery.com web site: http://www.frogpondpottery.com
"The whole aim of practical politics is to keep the populace alarmed, and
hence clamorous to be led to safety, by menacing it with an endless
series of hobgoblins, all of them imaginary." H.L. Mencken, 1925
Stephen Mills on sat 12 sep 98
>
>Just about as quick as a hydrometer and almost always more accurate as
>hydrometers don't always settle to the same place in a thick glaze or
>slip.
>
I always dunk my Glaze Hydrometer in water before putting it in the
glaze; it lubricates the surface, giving me accurate readings, and also
making it easier to read the scale.
Steve
--
Steve Mills
Bath
UK
home e-mail: stevemills@mudslinger.demon.co.uk
work e-mail: stevemills@bathpotters.demon.co.uk
own website: http://www.mudslinger.demon.co.uk
BPS website: http://www.bathpotters.demon.co.uk
Vince Pitelka on tue 15 sep 98
>Six months ago or so I posted a message about a hydrometer I found in the
>VWR Scientific Products catalog (800/932-5000 - www.vwrsp.com), which
>according to the description seemed especially appropriate for use with
>terra sig (and thin slips and glazes). I have not ordered this hydrometer,
>but all the specs are right. It is designed for testing small volumes of
>heavy liquids, is 6.5" (165mm) long, has a s.g. scale from 1.00 to 2.00, and
>costs $19.97 each - catalog number is #34640-207.
I just realized that I may have misled some people with the message above.
The specific gravity scale on this hydrometer only goes from 1.00 up to
2.00, which is ideal for terra sig, but will be of little use in checking
the consistency of glazes or casting slips, if you believe in using a
hydrometer for those applications. Just wanted to clarify this before
someone buys this hydrometer for the wrong application.
- Vince
Vince Pitelka - vpitelka@DeKalb.net
Home 615/597-5376, work 615/597-6801, fax 615/597-6803
Appalachian Center for Crafts
Tennessee Technological University
1560 Craft Center Drive, Smithville TN 37166
Vince Pitelka on wed 16 sep 98
>I just realized that I may have misled some people with the message above.
>The specific gravity scale on this hydrometer only goes from 1.00 up to
>2.00, which is ideal for terra sig, but will be of little use in checking
>the consistency of glazes or casting slips, if you believe in using a
>hydrometer for those applications. Just wanted to clarify this before
>someone buys this hydrometer for the wrong application.
OK, this is going to come across as REALLY confused. I wrote the above
message in a hurry after a personal email from someone complaining that this
hydrometer was not appropriate for glazes. I took them on their word, and
sent off a post without really thinking clearly about it. But now, after
coming to my senses, I TAKE IT ALL BACK!! If you DO believe in measuring
stoneware/porcelain glaze specific gravity with a hydrometer, this one WILL
work, because most such glazes weigh in with a specific gravity ranging from
1.4 to 1.8. Some will be beyond the useable range of this hydrometer, but
it should cover most needs. I promise not to change my mind on this again.
My appologize to anyone who is getting as confused as I must seem.
- Vince
Vince Pitelka - vpitelka@DeKalb.net
Home 615/597-5376, work 615/597-6801, fax 615/597-6803
Appalachian Center for Crafts
Tennessee Technological University
1560 Craft Center Drive, Smithville TN 37166
Linda Arbuckle on fri 18 sep 98
I think this has all come up someplace before, but...
hydrometers don't read accurately in a flocculated glaze. I always
flocculate my majolica glaze for better, more even application. Read
Frank Hamer on Flocculation and Deflocculation for the details. I
n a flocculated glaze, the clay platelets clump end-to-middle, and you
can within a range, just put your hydrometer in to whatever depth you
like, and it stays put.
Deflocculated slips (like sig) or glazes ( e.g. glazes containing soda
ash or lithium carb) have the clay particles slightly repelling each
other, and here a hydrometer seems to work fine.
--
Linda Arbuckle
Graduate Coordinator, Assoc. Prof.
Univ of FL
School of Art and Art History
P.O. Box 115801, Gainesville, FL 32611-5801
(352) 392-0201 x 219
e-mail: arbuck@ufl.edu
Joseph Herbert on tue 9 oct 01
Jim Karavias wrote: I've been looking for a hydrometer for sp. gr. range
of 1.000 to 2.000....
For pottery making purposes the precision of a "real" hydrometer is not
necessary or particularly useful. Most of what you really want to know is a
relative thing, like "what is the density of the slurry now as compared to
how it was when I first mixed this?" Because of the effects of the solid
particles suspended in the slurry, the liquid is "non-Newtonian" by a lot.
The standard floating hydrometer does not cope well with the solids and the
calibration, the thing you are paying that money for, is not accurate.
All is not lost. You can make a serviceable floating hydrometer from a
weighted stick or a sealed plastic tube with some ball bearings in it. Just
make some marks on it and record the floating level on your glaze recipe
card when you mix the glaze fresh. Later, you just take the same stick and
compare the current reading with the card and adjust accordingly.
Without any new equipment, you can just fill a standard measure (yogurt cup)
with slurry and weigh it. Record the weight of the standard amount on your
glaze card for future reference.
Good Luck
Joseph Herbert
primalmommy on thu 5 jun 03
Nice catch, dumpster diving! Here's something I figured out about
hydrometers:
I use mine for terra sigillata but I make really small batches. (I mix
up enough to half fill a clear 2 liter, clear plastic bottle. I write
all the details on the side in permanent marker, and can toss them in a
bag to take with me without worrying about breakage...) So how to use a
long hydrometer for a shallow batch of terra sig?
So I got a length of PVC pipe and pounded a cork into the bottom of it.
I fill it with terra sig (but not enough to overflow with the hydrometer
in it.) Then I can measure, and pour the TS back in the bottle.
I always embarrass my husband by bringing stuff home. Circumstance and a
generous father resulted in my driving a generic soccer-mom mini van..
but I carry a length of rope in the glove compartment and in the past
few months have driven around with bales of straw tied on top, an
abandoned dresser, a bunch of 6 foot broken banquet tables from a
dumpster by the church... wooden pallets to wire together for free
composters...
anyway nice work on the dumpster diving. We don't buy anything on credit
and as a result, people are leaving better computers/technology on the
curb than we have in our house!
Yours,
Kelly Averill Savino in Ohio (who just joined the naked raku message
board...)
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Lowell Barron on sun 21 mar 04
Dear Friends,
ENOUGH ENOUGH! For a relative newbie, PLEASE just tell me the simplest way
to figure out how thick to make the glaze especially the MC6G
ones....variegated blue, var. slate blue, licorice, Waterfall Brown in
particular. Also Rosie's or Randy's Red.
I was using the old finger in the glaze method but am not at all sure even
with it. When I was glazing at the Guild studio, I relied on someone else to
determine what consistency to make the glaze. Now that I am on my own I need
help.
Many thanks for all your help and sharing. Lowell Ann
Julie Moore on sun 18 mar 07
I have a handy home made hydrometer. It=92s a plastic straw I =
=91borrowed=92 from
a fast food place. I threaded a small nut onto the bottom of the straw =
as a
weight. The plastic seems to conform to the threads in the screw and it
stays put quite nicely. I then marked increments about =BD=94 apart on =
the
straw with an indelible marker and numbered each mark. When my glaze =
turns
out the way I want it, I stir it up well, measure with the hydrometer
(trying to set it into the glaze approximately the same way each time) =
and
write the number on the glaze bucket. This way I have only one tool =
(and a
backup) to keep track of and have the readings recorded for easy =
reference
when I mix up the next batch of that same glaze. This has worked very =
well
for me for years.
=20
Glaze on=85
Julie
Lee Love on mon 9 jul 07
On 7/9/07, Nancy Udell wrote:
> Hi John, Thanks for that advice and I do usually mix up my glazes
> without a hydrometer. But certain glazes, over time, get to another
> consistency due to evaporation even with a lid on, and I'd like an
> easy way of getting them back to where they were.
You could do a modification of what was mentioned: weigh the bucket
when you are finished glazing and write it on tap and put it on the
bucket.
This doesn't work for me with my base glaze, because I start
with glazing thin stuff with thick glaze, and add water as I glaze
thicker work. So, there is less water in the glaze in the begining
than there is at the end. The way you deal with this is to take all
excess water off the top of the settled glaze befrore you start
glazing. Then you add some back. I check the thickness of the
glaze on a test piece of bisque by dipping it and then scratching the
surface. This is good because you actually see the thickness of the
glaze with your eye. It also is good if your body is of differeing
thickness and bisque temp, as yo u often find in a wood kiln.
--
Lee in Mashiko, Japan
Minneapolis, Minnesota USA
http://mashikopots.blogspot.com/
"To affect the quality of the day, that is the highest of arts." -
Henry David Thoreau
"Let the beauty we love be what we do." - Rumi
Nancy Udell on mon 9 jul 07
Hi John, Thanks for that advice and I do usually mix up my glazes
without a hydrometer. But certain glazes, over time, get to another
consistency due to evaporation even with a lid on, and I'd like an
easy way of getting them back to where they were. Also sometimes I
have used a glaze that was thicker than I thought it should be and
gotten great results. I'd like to be able to measure the SG and get
back there. I have tried many times to use the "weigh a cup of water
and a cup of glaze" technique, and it just never seems to work for
me. I either spill the water or the glaze or they don't seem to be
exactly the same amount full. Was going to try the floating bottle
method, but a hydometer is so reasonable and since vince uses
one.... I thought why not. Interestingingly, in 1998 the hydrometer
was 19.95 according to Vince's post. Now it's about double that, but
if it works and can be used over and over, that seems ok to me. I
admit that I don't fully understand the difference betrween SG and
viscosity, but since i am not using floculants in my glaze, I;m
thinking I'll be OK...
Nancy in Santa Fe, where the dryness can change the SG of glazes very
quicky.
***
Weigh out equal
volumes of water and glaze, divide the weight of the water into the
weight of the glaze, and Voila!! you have the specific gravity or
density of the glaze. Add or remove water to adjust the density.
Vince Pitelka on tue 10 jul 07
Hydrometers generally work well for measuring density in all but the
thickest glazes, but it is important to remember that the scales are inexact
from one hydrometer to the next, so you must confirm glaze performance first
by the firing results, and then go with that same specific gravity in
subsequent batches of the same glaze, and repeat that process with each of
your glazes. You cannot tell someone "My cone 10 oatmeal glaze works best
at a specific gravity of 1.55," because their hydrometer will measure
differently and they will get different results. But for use within your
own studio, a hydrometer works well as a comparative reference for getting
repeated results once you establish the best hydrometer reading for each
glaze.
Remember that the thicker the glaze, the less accurate the hydrometer
reading. When I was making pots full-time in California I needed fairly
exact reproduceable results, and found that a glaze hydrometer worked well
for glazes ranging from 1.45 to 1.70 specific gravity.
- Vince
Vince Pitelka
Appalachian Center for Craft, Tennessee Technological University
Smithville TN 37166, 615/597-6801 x111
vpitelka@dtccom.net, wpitelka@tntech.edu
http://iweb.tntech.edu/wpitelka/
http://www.tntech.edu/craftcenter/
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