Kevin R. Biles on tue 14 aug 01
I'm new in this field and on this list. I am in the process of making
terra sigillata--had great luck getting layering using trisodium
phosphate as a deflocculator, but see that many recipes call for
Calgon. Can someone tell me which form and where you get it? Our small
town grocery stocks a "laundry booster" which contains phosphate, but I
wasn't sure that was what I needed.
I also see recipes calling for sodium silicate and /or soda ash.
While I'm at it, for the current projects, I don't need a high shine,
just a smooth, satin finish. In fact, since I am depending on others to
fire my pieces for me, I'm looking at cone 04-06, so will proably lose
some shine. The recipe I'm using (equal parts OM-4 and EPK with TSP)
calls for one 24 hour settling period, siphoning off the middle layer
(assuming you get a water layer on top), then letting that layer settle
for 24-48 hours. The middle layer has gradations and I am not sure how
much to take--I'm told 2/3-3/4, but there is quite a range in opacitiy
of the mix between those proportions. I have siphoned off what I
consider to be the best stuff but, as I leave the solutions for longer
periods, I get more settling and wonder if I could take more.
Also, how transparent is this stuff? I've read you can use it over
underglazes. Does the terra sig mute their colors? If you use it
(moderately) over a colored clay body, will it give a milky
appearance? Right now, I don't have the opportunity to run a lot of