Slip- Engobe Study in Clay and Glaze Chemistry Posted May 26 · Edited May 26 by glazenerd · Report reply Actually Mark, your email convinced me to make one more post. The reason I am disconnecting is at the bottom. I cut and pasted this from the Crystalline Glaze forum- to where I just posted it under my user name there. ------------- Actually Gordon, I have been reading about the effects of PH on ionic exchange; in part the theory behind a terra Sig. Norton (M.I.T.) and Lawrence & Buttons (Alfred) did the original studies on slip starting in 1948-1974. Norton actually started the whole sodium silicate/terra sig when he was studying the effects of PH on the water hull. He wrote the "stretched membrane" theory in 1948: the basis of modern slip chemistry. Norton describes the measured effects of sodium silicate in solution: resulting in a particle range from 0.14 to 0.57 microns..or in pottery terms 30,000 mesh. If you are a big terra sig person: first buy Taylor ball clay from a Old Hickory Clay Co. In Kentucky. OM4 has a median particle size of 0.67, and Taylor 0.31. Which means you will get over twice the payload for your efforts. With freight, Taylor will cost you 0.50 cents a lb- but they sell 50lb bags only. Second is an ionic charge trick I will teach you. Lawrence and a Buttons also wrote on the effects of temperature on ionic charge. At 60F, the ionic charge that suspends those fine particles potters want in terra sig drops by 1/3, which directly effects the amount produced. However, at 140F, the ionic charge is at its peak: which means the quality of fine particles held in suspension is much higher- resulting in more yield. The trick: heat the water to 135-140F ( but no higher), add your sodium silicate first- then your Taylor ( or OM4). In 1-2 hours when it cools back to room temp 75 or so. Siphon off the goodies as usual. You now have more sig in two hours than in 24 hours. So remember folks- you heard it here first. As other potters hack the info from this site and add it to theirs and claim a great discovery- you heard it hear first. Enjoy Gordon tom. - was going to make a CM article out of this... But hey. Several recent threads on image theft, cultural theft: but theft of intellectual property is never mentioned.