I recently made a batch of pottery using Sodium silicate to get crackled surface. Everything went extremely well.
A couple of days ago I decided to make another batch. I throw a piece, dry the porcelain surface a little with propane flame, apply sodium silicate or its mix with a slip, dry the layer with a heat gun and start stretching.
This time I only get vertical cracks that quite quickly become a way too deep. No fine cross pattern (spider web) at all. Same porcelain fresh from the box, same sodium silicate and SS/slip mix as before.
I tried thin and thick Sodium silicate layers, flamed and raw porcelain surfaces. The results are still exactly the same.
What I didn't try yet is leaving the SS crust a bit more moist. Also, this time I throw mugs, so I leave the porcelain walls thinner since I'm not going to expand them much. But even if I wanted, I couldn't expand them more because of the deep vertical cracks that rip the surface apart as soon as I overstretch it a bit.
While I was struggling with porcelain, my wife made a few hand built pieces out of stoneware, and didn't have this problem.
What do you think can be the cause?