Tom Wirt on tue 10 aug 99
Following my post re: specific gravity, I found out that the correct term
used by scientists now is DENSITY.....(mass per volume). Specific gravity
is gone.
Tom Wirt
Bill Aycock on wed 11 aug 99
Tom, (and others)
Fear not !! the difference is a quible. ( I am one of the worst quiblers,
therefore an expert) The difference is minute, and mostly in the minds of
the quiblers. Stricktly speaking, "specific gravity" is a reference to
water, as a standard, and the units are ** none **. It means this times as
dense as water.
Density, on the other hand, has units, and they are mass/unit volume, as-
Grams per cubic centimeter. The one I quible about is the use of weight
units per volume- as- Pounds per cubic foot. Stricktly speaking, this isn't
density, but specific weight.
There are so many specifications and catalogs out there with older sets of
units, that any attempt to "standardize" is doomed to a long waiting
(weighting ? ) time.
I was the resident expert (unofficial) on units of measure at the Rocket
plant where I spent most of my career. My absolute favorite specific weight
set of units is ** Tons per Tun ** it ranks right up with furlongs per
fortnight ( a velocity measure).
Bill- still working on the studio porch.(at 90+ degrees [F])
At 02:01 PM 8/10/99 EDT, you wrote:
>----------------------------Original message----------------------------
>Following my post re: specific gravity, I found out that the correct term
>used by scientists now is DENSITY.....(mass per volume). Specific gravity
>is gone.
>
>Tom Wirt
>
>
-
Bill Aycock --- Persimmon Hill
Woodville, Alabama, US 35776
(in the N.E. corner of the State)
W4BSG -- Grid EM64vr
baycock@HiWAAY.net
w4bsg@arrl.net
Tom Buck on thu 12 aug 99
Dear Bill on the Hill:
Now you really are quibbling, when you say SG has no units; you
know better... SG is referred to the density of water, whatever units you
use, and so although we never cite those units when we use the obsolete
term SG, the units are still there even if you (and others) ignore them.
So there! Use density please, and since most of us have gram scales to
weight out our glazes, there is no difficulty knowing that 310 grams for
200 millilitres means the slurry has a density of 1.55 g/mL, the proper
amount for dipping pots bisqued to C04.
Tom Buck ) tel: 905-389-2339
(westend Lake Ontario, province of Ontario, Canada).
mailing address: 373 East 43rd Street,
Hamilton ON L8T 3E1 Canada
Cheryl L Litman on fri 13 aug 99
Tom,
Speaking of the proper dipping density for pieces bisqued to 04, what is
the proper density for other temps? Where do you find this info? What
about proper density for brushing glazes? I've heard some of you guys
discuss this before, but does it come from your personal trial and error
or is there something like limit formulas somewhere for this?
TIA
Cheryl Litman
Somerset, NJ
email: cheryllitman@juno.com
On Thu, 12 Aug 1999 14:59:16 EDT Tom Buck writes:
>
>----------------------------Original
>message----------------------------
>Dear Bill on the Hill:
> Now you really are quibbling, when you say SG has no units;
>you
>know better... SG is referred to the density of water, whatever units
>you
>use, and so although we never cite those units when we use the
>obsolete
>term SG, the units are still there even if you (and others) ignore
>them.
>So there! Use density please, and since most of us have gram scales
>to
>weight out our glazes, there is no difficulty knowing that 310 grams
>for
>200 millilitres means the slurry has a density of 1.55 g/mL, the
>proper
>amount for dipping pots bisqued to C04.
>
>Tom Buck ) tel: 905-389-2339
>(westend Lake Ontario, province of Ontario, Canada).
>mailing address: 373 East 43rd Street,
> Hamilton ON L8T 3E1 Canada
Cheryl Litman
Somerset, NJ
email: cheryllitman@juno.com
John K Dellow on fri 13 aug 99
Hay Tom ,1.55 g/ml might be ok for a feldspathic temmoku but a
bit thick for rutile glaze ! :).
Tom Buck wrote:
>
> ----------------------------Original message----------------------------
> Dear Bill on the Hill:
> Now you really are quibbling, when you say SG has no units; you
> know better... SG is referred to the density of water, whatever units you
> use, and so although we never cite those units when we use the obsolete
> term SG, the units are still there even if you (and others) ignore them.
> So there! Use density please, and since most of us have gram scales to
> weight out our glazes, there is no difficulty knowing that 310 grams for
> 200 millilitres means the slurry has a density of 1.55 g/mL, the proper
> amount for dipping pots bisqued to C04.
>
> Tom Buck ) tel: 905-389-2339
> (westend Lake Ontario, province of Ontario, Canada).
> mailing address: 373 East 43rd Street,
> Hamilton ON L8T 3E1 Canada
--
John Dellow "the flower pot man"
Home Page http://www.welcome.to/jkdellow
Tom Wirt on sat 14 aug 99
From: Cheryl L Litman
Subject: Re: Specific Gravity...errr, Density
> ----------------------------Original message----------------------------
> Tom,
>
> Speaking of the proper dipping density for pieces bisqued to 04, what is
> the proper density for other temps? Where do you find this info? What
> about proper density for brushing glazes? I've heard some of you guys
> discuss this before, but does it come from your personal trial and error
> or is there something like limit formulas somewhere for this?
>
Hi Cheryl....
As far as I know, the proper density for any given glaze will vary depending
on how you apply the glaze, the bisque temperature, the glaze recipe itself
(and certain ingredients in it). It really is a trial and error process, as
far as I know.
Typically, there is about as much weight in water in a glaze as there is
solid ingredients. A 20,000 gram batch is about 44 lbs. and takes about 5
gallons of water @ about 8 lbs. per gallon. That's at least a starting
point for dipping and pouring.
Also be aware that some glazes will FEEL like they've got too much or too
little water depending on ingredients. We have a Kaki that feels almost
like thick water, yet its density is higher than the moonlight which feels
almost like mud.
If you're not sure the first time you mix up a recipe, use less rather than
more water initially, it's easier to add than to subtract. If you get too
much water, then you're into settling and decanting.
Then to add more confusion, you get into flocculation and deflocculation.
Better run to the archives on that one.
I know it's not much help,
Tom Wirt
John Rodgers on sat 14 aug 99
My experience with this subject is, that for application purposes, as in
testing glazes by doing firing tests, glazes should also be tested for the
best viscosity and specific gravity for the particular application. The
test for the best method of application is done along with the glaze.
Ask the question, "Does this glaze work best when dipped, sprayed, or
brushed on, and at what viscosity and specific gravity ande on what clay
body?"
So, the tests are necessary, because of the number of variables. Run a
series of tests, keeping track of the specific gravity (density) of the
glaze and it's viscosity, for each application. But be sure you DO keep
track of the numbers, for they will set you free.
Once you have the specific gravity nailed for each kind of application, and
the related viscosity, you are home free. If you wrote it down, and kept
your test tile or whatever, you can always repeat it when setting up to do
glazing.
Once you seem to have the glaze specific gravity right, if it seems the
viscosity of the glaze is low or runny(non-scientific term) you can add a
tiny(and I do mean tiny - another non-scientific word) bit of epsom salts
solution.....like one milliliter at a time. Of course this depends on the
volume of glaze you are mixing....Say 5 gallons vs 500 milliliters of
glaze. Add the epsom salt solution, the glaze viscosity will increase.
If the glaze seems to viscous, a tiny( and again I DO mean tiny) bit of
sodium silicate can be added. Because nearly all glazes have some clay in
them, the sodium silicate will ionize and the resultant electrical charge on
the clay particles will cause them to repel each other and the glaze
becomes more slippery and fluid. That way you get a decrease in viscosity
without adding water.
To check the viscosity, you will need to time the rate at which a given
amount of glaze runs through a specific size orifice(hole). There are
plastic viscosity testers available from the various clay supply houses.
They provide the simplest, easiest way to test the viscosity. Using the
sweep second hand on your watch or clock, just time the rate at which the
container empties. That volume per unit of time measured reflects the
viscosity. The lower the time, the lower the viscosity.
If the specific gravity is right on, but the flow rate is low (high
viscosity), a small amount of sodium silicate is called for. That will
loosen the glaze to flow faster. If the flow rate is high, (low viscosity -
runny) epsom salts will thicken the glaze and slow its flow.
The real trick is to first get the ratio of the water to the dry glaze
materials fixed. That sets the specific gravity. Then work on adjusting the
viscosity. If, after setting for a time, the glaze seems thick, check the
specific gravity before doing anything else. Many times just stirring is
sufficient to loosen the glaze for application. No silicate, epsom salts, or
water is necessary. If you are dipping, all these relationships will change
as the glaze is used up. But now you know how to adjust them.
A couple of final notes.
(1) Most glazes settle out over time and leave water floating on the
surface. If you have gotten the specific gravity out of balance...ie, to
much water so the specific gravity is two low, this is the time to correct
the problem. With a big sponge, simply soak up some of the water on the
surface. Repeated several times, this will move the specific gravity toward
the high side, and now you can begin to adjust the glaze.
(2) Be extremely cautious in adding any sodium silicate. Even the tiniest
bit to much can result in the glaze ingredients settling to the bottom of
your bucket almost instantly.
Hope this helps with getting the best glazes ever!!
John Rodgers in New Mexico.
Cheryl L Litman wrote:
> ----------------------------Original message----------------------------
> Tom,
>
> Speaking of the proper dipping density for pieces bisqued to 04, what is
> the proper density for other temps? Where do you find this info? What
> about proper density for brushing glazes? I've heard some of you guys
> discuss this before, but does it come from your personal trial and error
> or is there something like limit formulas somewhere for this?
>
> TIA
> Cheryl Litman
> Somerset, NJ
> email: cheryllitman@juno.com
>
> On Thu, 12 Aug 1999 14:59:16 EDT Tom Buck writes:
> >
> >----------------------------Original
> >message----------------------------
> >Dear Bill on the Hill:
> > Now you really are quibbling, when you say SG has no units;
> >you
> >know better... SG is referred to the density of water, whatever units
> >you
> >use, and so although we never cite those units when we use the
> >obsolete
> >term SG, the units are still there even if you (and others) ignore
> >them.
> >So there! Use density please, and since most of us have gram scales
> >to
> >weight out our glazes, there is no difficulty knowing that 310 grams
> >for
> >200 millilitres means the slurry has a density of 1.55 g/mL, the
> >proper
> >amount for dipping pots bisqued to C04.
> >
> >Tom Buck ) tel: 905-389-2339
> >(westend Lake Ontario, province of Ontario, Canada).
> >mailing address: 373 East 43rd Street,
> > Hamilton ON L8T 3E1 Canada
>
> Cheryl Litman
> Somerset, NJ
> email: cheryllitman@juno.com
Ray Aldridge on sat 14 aug 99
At 03:43 PM 8/13/99 EDT, you wrote:
>----------------------------Original message----------------------------
>Tom,
>
>Speaking of the proper dipping density for pieces bisqued to 04, what is
>the proper density for other temps? Where do you find this info?
Not to speak for Tom, but in my opinion, trial and error is the only
workable approach. Every clay will have a slightly different absorption at
a given work heat bisque, and every glaze will look different depending on
the thickness of application. Other factors will be the thickness of the
bisque (thick bisque sucks, so to speak) and the length of time the pot is
held in the glaze. And then there's raw-glazing, with another set of wild
cards.
Ray
Evan Dresel on sat 14 aug 99
There are 2 kinds of scientists, those who get a kick out of
"dimensionless" numbers and those who like to keep all the dimensions
explicit, when possible. I'm the latter kind. The term specific
gravity is still used, sort of a quaint anachronism. Specific gravity
is the mass per volume of an object divided by the mass per volume of
pure water. The mass per volume of water is 1 kg/L at 25 C so using the
metric system, it's all the same. That's why specific gravity has no
"units" or is dimensionless: kg/L divided by kg/L cancels out the units
-- would be the same if you measured in oz/quart. Still, keep the units
in and you will be really clear what you are talking about. The term
specific gravity is still used, sort of a quaint anachronism. I guess
I'm crass when I say something has a specific gravity of 2.6 kg/L.
Should say density but s.g. has a nice ring.
-- Evan who is under major scientific stress right now and finds ClayArt
more relaxing than beer.
Tom Wirt wrote:
>
> ----------------------------Original message----------------------------
> Following my post re: specific gravity, I found out that the correct term
> used by scientists now is DENSITY.....(mass per volume). Specific gravity
> is gone.
>
> Tom Wirt
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