Kim Lindaberry on wed 18 aug 04
Hello All,
After several years off the ClayArt list I am back to it.
The adjunct instructor that had been teaching, and more or less managing the ceramics studio, at
my school has moved onto a full-time position elsewhere. That is great for her, but I now find
myself taking a more active role in managing and teaching in the ceramics studio. This of course
includes ordering all the glaze materials AND making sure our glazes are mixed. So that is where
my primary questions are focused for now. We have always mixed up batches of ^04 & ^6 glazes
in 5 gallon buckets.
How many grams would you recommend for a batch of glazes, 3,000 - 5,000?
One thing I've always had a somewhat difficult time with is approximately how much water to add
to a 3,000 or 5,000 gram batch? This is of course going to vary depending on the quantity being
mixed and the specific composition of the glaze, but a ballpark amount of water would be helpful.
That then leads me to my next question. It seems like our studio glazes have always been
somewhat inconsistent. Lids get left off the buckets and they dry out, or students dump extra
water in so they can increase the volume of a small amount so they can dip a piece in. I have
bought a hydrometer to help us at least be reasonably consistent BUT what reading on the
hydrometer would you recommend when first mixing up a batch for dipping?
Thanks for any assistance,
cheers,
Kim
Ben Shelton on thu 19 aug 04
>
>That then leads me to my next question. It seems like our studio glazes
have always been
>somewhat inconsistent. Lids get left off the buckets and they dry out, or
students dump extra
>water in so they can increase the volume of a small amount so they can dip
a piece in. I have
>bought a hydrometer to help us at least be reasonably consistent BUT what
reading on the
>hydrometer would you recommend when first mixing up a batch for dipping?
>
>Thanks for any assistance,
>
>cheers,
>
>Kim
>
Well, you have two issues here. One is measuring the water content of the
glaze. The second is determining what water content is right for each
glaze/application method.
The BEST way to measure water content is specific gravity. (IMHO)
I assume you have a triple beam balance that you are using for weighing out
glaze ingredients. You'll also need a graduated cylinder or other tall,
narrow container. I used a shampoo bottle with the top cut off and a line
drawn on it for years. You put in a set volume of mixed glaze (say 300
mililiters) and weigh it on your balance. do the math to find the mass per
volume.
Now comes the big question. What specific gravity will be "BEST" for each
glaze?
For me, this is always a trial and error exercise. Because all potters
methods vary, and all pots vary, this can be a hard number to nail down.
Mix up a 300g test batch, to measure the glaze's specific gravity, make a
test tile, add water, repeat. Mark the tiles so you'll know which specific
gravity worked best!
Fire the tests and see what looks best. Then use that data to adjust your
studio glazes specific gravity.
As far as what batch size to mix up, if you have verified the materials are
correct by testing (say a 300gram batch) I ususally mix a 10,000g batch to
fill a 5gal bucket and mix another 5000 when the bucket gets about 1/2
empty. (don't mix them until you have run a test of the new batch,
sometimes we mix things up incorrectly by mistake, been there, done that)
Don't let your students monkey with the glazes. Explain that you are
working hard to provide reliable results for everyone. If someone needs
more of a certain glaze, they need to speak to the studio tech instead of
adding water to glazes willy nilly. Not only does that make headaches for
you but for all the other students too. Besides you could use it as a
teaching/learning opportunity if someone is curious about glazes,
chemistry, specific gravity etc etc. I always enjoyed teaching folks about
stuff like that.
Good luck and have fun
Ben
Greg Marshall on thu 19 aug 04
Kim,
I have found that about a 10,000 gram batch of glaze will fill a 5 gallon bucket. Most of my glazes are measured out into 6,000 to 8,000 gram batches so that I can add a new batch when the bucket gets down to about 1/3. My rutile blue glaze batch adds up to 6,518 grams. I add 6 quarts of water to this batch and it makes it really close to the thickness I want. Rather than use a hydrometer, I prefer to weigh the glaze to determine the proper thickness. I use a plastic 2 cup measuring cup, fill the cup to the 2 cup line and weigh it. It will take some trial and error to determine exactly what each of your glazes needs to weigh to be the thickness you like for that glaze. For example, my rutil blue glaze needs to weigh 770 grams in my measuring cup to be the thickness I like. If it's thicker it will weigh more and if it's thinner it will weigh less. This is similar to determining the specific gravity of the glaze which you could do using any container. I think this is a more a
ccurate way to control the thickness of a glaze.
Good luck.
Greg at the foot of Pikes Peak.
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