Phil Smith on mon 19 jan 04
Hi Folks,
One cc of water weighs one gram.
If I weigh 50 cc's of glaze and it weighs 65 grams I should have 15
grams of glaze materials in there. 1.3.
Water divided by total weight = .76923 percent water.
If I were to weigh out 1814.369(4 lbs) wet glaze.
1814.369 x .7692 = 1395.613 water
418.7 should be glaze materials.
Recipe calls for 2 percent cobalt.
.02 x 418.7 = 8.374 grams.
I would add 8.37 grams cobalt to my 4lbs wet glaze.
Phil...
Zsuzsa Koltay on mon 19 jan 04
I have a question that is probably quite basic but it's stumping me.
Is there as easy way to correlate dry weights and wet weights when
formulating glazes?
Here's what I'd like to do: mix up a large batch of some base glazes and
then later take smaller portions of the mixed base glazes and add different
colorants to those. But the amount of colorants is given as a dry weight,
so how can I go about doing this? Or is this a bad idea?
Thanks,
Zsuzsa
Bruce Girrell on mon 19 jan 04
> Is there as easy way to correlate dry weights and wet weights when
> formulating glazes?
Oh, hey! I just did that. It may seem basic, but it's not. What you need is
called Brongniart's formula and can be found in Hamer and Hamer. Depending
on what you need, the formula may have to be rearranged (left as an exercise
for the reader). I needed to compute how much water to add to a specific
amount of dry ingredients to result in a desired specific gravity of glaze.
Someone has created an applet to compute it for you:
http://www.morrigancraftpottery.co.uk/brong.html
Not everything in the applet is intuitively obvious unless you play around
with the formula a little. Look for "formula, Brongniart" in Hamer and Hamer
or do a search in the archives for Brongniart. I wish I had more time to
explain it right now, but I don't. Try doing the algebra on your own and if
you have problems make another post.
Bruce "off to another exciting meeting" Girrell
John Rodgers on mon 19 jan 04
You can probably use Bronigarts (sp) Formula to calculate dry weight in
a wet glaze. Sorry, I don't have it handy, but I mention the name as a
resouce.
I don't bother. I simply make 100 or 1000 gram batches to test, and I
start from scratch. I have found it easier that way, and more accurate.
Just my way of doing!!!
Regards,
John Rodgers
Chelsea, AL
Zsuzsa Koltay wrote:
> I have a question that is probably quite basic but it's stumping me.
>
> Is there as easy way to correlate dry weights and wet weights when
> formulating glazes?
>
> Here's what I'd like to do: mix up a large batch of some base glazes and
> then later take smaller portions of the mixed base glazes and add
> different
> colorants to those. But the amount of colorants is given as a dry
> weight,
> so how can I go about doing this? Or is this a bad idea?
>
> Thanks,
> Zsuzsa
>
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>
Snail Scott on mon 19 jan 04
At 10:31 AM 1/19/04 -0500, you wrote:
>Here's what I'd like to do: mix up a large batch of some base glazes and
>then later take smaller portions of the mixed base glazes and add different
>colorants to those. But the amount of colorants is given as a dry weight,
>so how can I go about doing this? Or is this a bad idea?
I keep my base engobe in dry form, in a big
container, and only add water after I've measured
out an individual batch and added my colorants.
No worries about solubility, either.
If you'd rather keep your base in wet form, just
weight the bucket, subtract the tare weight of
the bucket itself, and compare with the dry
weight. (More reliable than a rule-of-thumb
average estimate.) Then you'll know what proportion
of the glaze is water. So, when you ladle out a
small amount to modify, just weigh it, and
subtract the same proportion. Then you'll know
what the dry weight would have been, so you can
add colorants in the proper percentage.
-Snail
Dave Finkelnburg on mon 19 jan 04
Zsuzsa,
You could solve this problem from first principles...but there is also a
formula: The grams of dry solids in any sample of glaze = (weight of sample
in grams minus volume of sample in milliliters) times 1.6.
NOTES: The 1.6 is based on my assumption that the density of your glaze
ingredients is approximately 2.67, which is true for most porcelain and
stoneware glazes but NOT true for fritted lead glazes.
This was originally called Brogniart's Formula, after a
French slip-caster who developed the formula for working with casting slips.
Originally the formula worked with ounces and pints. To avoid confusion I
prefer grams and milliliters.
By the way, is milliliters the current politically correct
unit of volume? The last time I wrote about this I think I said cubic
centimeters and received a note off-list explaining that I was, as our kids
frequently remind me, terribly out of date. -) If I have it backwards
please let me know. Thanks!
We potters run into this problem whenever we have a wet batch of glaze
and want to add x-percent by weight of some ingredient. The first things we
need to know are the weight and the volume we are working with. I like to
use a graduated cylinder to measure the volume of a well-mixed glaze sample
and then I weigh that volume on a gram scale. While it isn't so easy to
weigh a bucket or a barrel of glaze, if you have done the above you have the
density of the glaze -- its' weight per unit volume. Then if you can
estimate the volume of the glaze you can multiply that by the density to get
the total weight of the wet glaze. Then it's just simple arithmetic to
calculate the weight of the dry glaze ingredients in your sample, bucket or
barrel.
Good glazing!
Dave Finkelnburg
----- Original Message -----
From: "Zsuzsa Koltay"
Sent: Monday, January 19, 2004 8:31 AM
> Is there as easy way to correlate dry weights and wet weights when
> formulating glazes?
Paul Herman on tue 20 jan 04
Phil,
I'm curious how you get the 15 grams of glaze materials compressed into
zero volume. Seems like it would take a lot of work....
Best wishes,
Paul Herman
Great Basin Pottery
Doyle, California US
http://www.greatbasinpottery.com/
----------
>From: Phil Smith
>To: CLAYART@LSV.CERAMICS.ORG
>Subject: Re: dry vs. wet weight for glazes
>Date: Mon, Jan 19, 2004, 5:59 PM
>
> Hi Folks,
> One cc of water weighs one gram.
>
> If I weigh 50 cc's of glaze and it weighs 65 grams I should have 15
> grams of glaze materials in there. 1.3.
> Water divided by total weight = .76923 percent water.
Phil Smith on tue 20 jan 04
Dear Dave,
You wrote:
>In your example, you have overlooked that in the glaze the dry
>ingredients have volume. So if there are really 15-grams of solids, they
>will have a volume of 15/2.65=5.7 mls or ccs and there are only 44.3 mls of
>water.
I had the thought that "this is way to easy"
I use that reasoning to mix my glaze and keep it the same.
"Mix to 1.3 hold for 3."
In my haste I had'nt considered the materials occupied space in the cc.
I'm learnin.
Would you be so kind as to give me the long Version?
Other folks might be interested as well.
Thanks.
Phil...
Gary Elfring on tue 20 jan 04
ZK> Is there as easy way to correlate dry weights and wet weights when
ZK> formulating glazes?
ZK> Here's what I'd like to do: mix up a large batch of some base glazes and
ZK> then later take smaller portions of the mixed base glazes and add different
ZK> colorants to those. But the amount of colorants is given as a dry weight,
ZK> so how can I go about doing this? Or is this a bad idea?
If you plan ahead, this is easy to do. You just need a graduated
cylinder. I might make a 400 gram test batch of a glaze, with no
colorants. Once it is wet, just measure how many ml the batch is in
your graduated cylinder. Divide the batch up into 4 separate batches
all of equal sizes (in ml). Now you have four 100 gram batches to
experiment with. (So if the 400 gram batch had a volume of 600 ml,
then each 100 gram batch would have a volume of 150 ml.)
--
Best regards,
Gary
Paul Lewing on wed 21 jan 04
on 1/19/04 7:31 AM, Zsuzsa Koltay at zk10@CORNELL.EDU wrote:
> Here's what I'd like to do: mix up a large batch of some base glazes and
> then later take smaller portions of the mixed base glazes and add different
> colorants to those. But the amount of colorants is given as a dry weight,
> so how can I go about doing this? Or is this a bad idea?
This is a good idea. Or at least I do it all the time, so I assume it's a
good idea.
Here's how I do it. I have a small mixer that I mix up 100g test batches
in. The first few times I made them, I marked where on the beaker 100g of
wet glaze came with a pencil. After a few, I made a mark where the average
of the volumes came, with a marker. You can also just dump your next 5 or 6
test batches into a measuring cup and see where they come.
So now when I want a 100g batch of a base glaze to color or test colorants
in, I just fill the beaker up to that point and assume it's 100g. It's not
precise, but it's close enough that you'll never notice the difference.
Paul Lewing, Seattle
Kathy Greaves on wed 21 jan 04
>>Can Brongniart's formula account for floculation/defloculation or gelling
of the glaze?
Russel<<
Using the specific gravity addresses the issue pretty well, though I expect
a glaze with 4% or more of bentonite (lots of expansion/jelling) might throw
things off a bit. To repeat, the basic formula is (#gms. per 100 ml - 100)
x 1.67 = #gms. dry wt. per 100 ml of glaze. This assumes a relative density
of 2.5.
It does have a modification for those glazes with low solubility. For the
glazes with low solubility you would use a relative density of 3.0. This
translates to (#gms. per 100 ml - 100) x 1.5 = #gms. dry wt. per 100 ml of
glaze.
Thanks, Clayarters, for alerting me to the formula! I had used my own
reasoning before, and I came up with similar results. What I reasoned was
that most glazes have about 90 ml of water for every 100 gm dry ingredients.
In that case, you could weigh 100 ml glaze and multiply the result by .55 to
get the dry ingredients. If you have a high clay content glaze, you would
need to mix it 50/50 with water so it's not too thick; so then you would
multiply by .5 for the dry ingredient content. Glazes that won't suspend
well would only get 80 ml water per 100 gm on average, so I'd multiply the
100 ml glaze weight by .6 to get my dry ingredient wt per 100 ml. Now, if
only I could remember not to add too much water when I mix those glazes up
in the first place!
Kathy Greaves
Sacramento, Ca
Dave Finkelnburg on wed 21 jan 04
Russel Fouts asked,
> Can Brongniart's formula account for floculation/defloculation or
gelling
> of the glaze?
In a word, no. Glaze flocculation, deflocculation and gelling are
caused by glaze chemistry. Brogniart was just measuring slip density.
Density of a slurry does affect the rate at which solids settle in that
slurry, including in a glaze. However flocculation and deflocculation are
the result of ions and molecules attracted to or repelled by the solids in
the slurry. The attachment and repulsion are the result of electrostatic
forces. Those forces depend on the kinds of solids present, and
particularly on the specific surface area of the solids. Clays play the
major role in flocculation and deflocculation of glazes. Density is simply
a physical measure of mass per unit volume.
This is really quite complex, and not completely understood by any
means. While there are many sources of information about this, the best
(most easily understood) explanation I have read of the surface chemistry
involved is in "Ceramic Science for the Potter, 2nd Edition," by Lawrence
and West (available from Axner). The authors grossly oversimplify the
subject, which is why I was able to follow what they wrote! :-)
Good glazing!
Dave Finkelnburg
Russel Fouts on wed 21 jan 04
Bruce
>> What you need is called Brongniart's formula and can be found in Hamer
and Hamer. <<
Can Brongniart's formula account for floculation/defloculation or gelling
of the glaze?
Russel
Russel Fouts
Mes Potes & Mes Pots
Brussels, Belgium
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