The first is a cone 6 snowflake crackle from John Britt/ Hard to see it in this phone camera pic but it really does have a nice crackle. I didn't get the snowflake effect but I suspect it wasn't thick enough.
This one is a cone 6 oil spot with a cover glaze, again both are from John Britt. This turned out great. I just used 11% zircopax as a colorant. I have test batches mixed with crimson stain and copper carbonate.
Speaking of tests... this was my morning. All are different base glazes or existing glazes I have used in the past. I want to get a baseline set of tests then start tweaking from there. There are 4 different iron reds in that picture. A number of ash glazes and some strontium matte glazes.