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terra sig questions - hydrometers

updated wed 10 may 00


Vince Pitelka on tue 9 may 00

At 12:20 AM 5/8/00 EDT, you wrote:
>----------------------------Original message----------------------------
>Hydrometers are available from any auto supply store. And yes, you need one.
>They cost between $2 and $3.
>Lynne Berman, a grateful clayart student of Vince's

Thanks Lynne, but for anyone wanting to use a hydrometer to prepare terra
sig, I suggest you spent the big bucks ($20 to $40) and buy your hydrometer
from a laboratory supply house. As Tom Buck has pointed out, hydrometers
are inherently inaccurate, and cheap ones are not worth bothering with. The
kind of hydrometer you want is the kind that floats in the liquid, where you
read the scale at the point where it emerges from the liquid. Hydrometers
do a good job on thin suspensions like terra sig, but are no good for
thicker suspensions like glazes. The thickest suspension I ever try to
measure with a hydrometer is the initial 1.2 specific gravity in my terra
sig process. The final terra sig, as I use it, is usually around 1.15 s.g.

It is important to experiment with the terra sig and see what consistency of
suspension works best for you. Hydrometers are inherently inaccurate, so
when I recommend 1.2 s.g. for the initial suspension, and you prepare it to
that s.g., your hydrometer might be way off when it gives that reading.
Once you find a consistency that works good for you, it gives you a basis
for comparison for preparing subsequent batches.
Good luck -
- Vince

Vince Pitelka
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