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sg and hydrometers and pint weights

updated tue 30 apr 96


Bill Aycock on mon 15 apr 96

It should NOT take a rocket scientist to be worried at the misunderstanding
of specific gravity measurements as exhibited by statements from Don and
Robert. Both made statements that are contrary to the laws of nature.

Adding electrolites or defloculants to glazes in small quantity DOES NOT
change the SG significantly. They DO change the viscosity and the Rheology.

A measure of Specific Gravity taken *!!* properly *!!* with a floating
device such as a Hydrometer is a good means of controlling the glaze content
of your mix. Weighing a cup of the mix is also a good way.

High viscosity and "gelled" slurries will effect the measurements taken
with a hydrometer if care is not taken to make sure the instrument is free
to move up and down. This may involve stirring the mix (if it is
Thixotropic) or waiting a while for the gadget to move.

The flow properties, tendancy to settle, and "feel" of some glazes (and
slips) can be changed drastically with electrolites, without changing the SG
a measurable amount.

The possibility to "add more clay" is due to changes in Rheology, not
Specific Gravity.

Bill- finished with the IRS (for now) on Persimmon Hill.