|Monthly Tech-Tip |
The clay is Plainsman Snow fired at cone 04. August 2022 by Nina Berinstein. Very thin and light pieces can be made without danger of warping during firing (because this clay as zero fired shrinkage). This piece was treated with Mod Podge, this has sealed it against water penetration and not affected the appearance or texture.
The right side of this bisque-fired clay bar (which has about 15% porosity) has been surface-treated with a silicone sealant. It repels the water, the drop rolls around on the surface if I tilt the bar. The drop on the left side absorbed into the clay in seconds.
This body has high porosity, almost 25%. It is L4410P, a dolomite-based low-fire whiteware, Plainsman Clays makes this as a product named "Snow". But this high porosity has some advantages, one of them is that it soaks up silicone sealer well. The slip-cast piece on the left was sealed (you can see the surface sheen) and it is impermeable to water penetration (the glaze is not crazed so water cannot penetrate there either). The piece on the right soaks up water readily (on the lower unglazed portion). Sealing this specific body is doubly important because the dolomite particles within can rehydrate over time, especially in damp climates, causing pieces to crack. Even the foot rings of functional pieces should be sealed, not just to prevent hydration but also waterlogging.
ModPodge clay sealer
Terra Sigilatta is a sedimentation process used by potters to remove coarse particles from a clay powder. It enables burnishing and gloss surfaces without the use of glaze.