So here's another jar with the black slip and drawing through the glaze. I made a new tool, which has one larger digit. I thought the bolder strokes would make the deco stand out a bit more, but i didn't know what to draw and in the end it was a bit difficult to use.
I tried a slightly different firing this time. Only went up to 1060 but increased the soak to about 30 minutes. The slip is blacker than the last one anyway as it had more oxides in it - they've come to the surface a bit more and it's now a bit metallic, which I don't mind. Overall, it's not as nice as the other one.
However, it has this:
Looks like shelling but it isn't. It's a blow-out. Small but enough to ruin a pot. I keep finding small bits of gravel in my clay. I'm not sure whether it's me that has introduced it, or whether it's from the supplier, but it's annoying. I'm sure a few bisque explosions have been caused by it.