JCullen845@AOL.COM on sat 26 aug 00
Tom, you're the greatest.
This question comes to mind everytime I mix a new glaze. that's about
everytime I do a glaze firing. I spray my glazes and have use a hydrometer, a
fiingernail, and a seat of the pants questimate. Sure things get glazed but,
what about that glaze that goes on too thin? Or too thick, rarely a problem
with spraying.
Thanks for answering this question in a concise, intelligent and easy to
follow manner.
KEEP CENTERED
Cullen
Naperville, Illinois
Jonathan Kaplan on sun 27 aug 00
Hydrometers do not, repeat, DO NOT measure the specific gravity of glazes
and casting slips accurately. I can take 100 readings with a hydrometer and
100 different readings.
Here is a simple accurate, and dependable method of measuring the specific
gravity of glazes and casting slips.
1. Find a narrow mouthed container or a necked container such as a pint jar
from commercial glaze or an Erlynmeyer or Florence flask.
2. Weigh the container and record the weight.
3. Fill the container with water up to the top and try to eliminate the
miniscus by slightly overfilling it so that it domes at the top.
4. Weigh the container with the water, subtract the weight of the container
and record this weight. This is the weight of the volume of water
contained in your container.
5. Fill the container with your glaze or casting slip.
6. Weigh the container with the slip or glaze.
7. Subtract the weight of the container from that total
8. Divide that weight by the weight of water (from above) and you will have
an accurate reading of specific gravity.
And yes, for you very exacting types, I assume that everyone will be
working at STP (standard temperature and pressure) and even though that is
not really true, the above method of obtaining SG is on hell of alot more
accurate than anything I know for potters outside of using scientific
testing apparatus.
For example, we use a container from Amaco Velvet Underglaze, more or less
1 pint
container weight 38 grams
weight of container with water 622 grams
thus weight of water in container is 584 grams
same container with our terra cotta casting slip 1076 grams
less weight of container (38 grams) is 1038
divide that weight (1038) by the weight of the water (584)
and the specific gravity of that slip is 1.77
Easy Huh? And far more accurate.
Jonathan
Jonathan Kaplan, president
Ceramic Design Group
PO Box 775112
Steamboat Springs CO 80477
voice and fax 970 879-9139
jonathan@csn,net
http://www.sni.net/ceramicdesigin
Plant Location:
1280 13th Street Unit 13
Steamboat Springs CO 80487
(please use this address for all deliveries via UPS, comman carrier, FEd
Ex, etc.)
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