26/03/2026
I have had a bit of a disaster...I was going to smash these pots up, but they would do for putting plant-pots in, or for dog-bowls. They are mostly OK on the inside...but they have blisters on the outside which leave sharp edges when you burst them. First come, first served!
For potters who might be interested in what happened... It is a classic case of trying to make things better whilst actually making them worse.
The Germans have a word for it..."verschlimmbesserung"...and the US military have an acronym...SNAFU.
I was trying to resolve a problem with being unable to get a thick enough coat of slip on my mugs without them taking on too much water and collapsing. I like to throw thin, full-bellied shapes and I was having failures with either a slip-coat that was too thin, or else with slumping. My attempted solution was two-fold. My slip is 100% Hiplas 71. I calcined 20% of it to increase the proportion of solids, raw clay having a proportion of "combined water" which calcined clay does not. Then I changed my clay for one which has no sand, my regular clay having 20% sand. My reasoning being that wet sand has no structural strength to withstand additional wetting, whereas clay does. All was well and good during the making, my pots withstood a thicker slip-coat without becoming too limp and I was able to throw well with the smoother clay. But what I had failed to take seriously was that I had interfered with the shrinkage rates of both the clay and with the slip. These shrinkage rates need to be fairly equal so that the slip shrinks more-or-less ,the same amount as the clay that it coats. I had REDUCED the shrinkage of the slip by adding pre-fired, non-shrinking material, and I had INCREASED the shrinkage of the clay by reducing the non-clay content...sand. My slip was shrinking less than my pot and, like a wetsuit that has become too big for the surfer who has lost weight, it was bulging out and forming air-filled blisters. Let that be a warning for you! If you are a potter, test, test, test before you make any big changes...and if you are a surfer...don't skip that hearty breakfast...
