Friday, 9 May 2014

Same Clay but Different

I've never come across this before.

While I was assembling an oval bonsai pot, I noticed that the bottom layer of clay seemed to be a lighter colour than the ovals sides. Oh I thought,.... perhaps the sides are just that little bit dryer than the bottom. I need to be careful as its quite important to have everything the same level of dryness when joining pieces.

Its just the bottom layer that's different, the darker area above is where the clay was compressed on the join and has got slightly burnished a bit.

I carried on and completed the pot. However, I kept looking at the difference in colours and thought that perhaps in the morning when the moisture level evens out it will all look the same.

I waited..... and waited....checked and rechecked, and no the clay colour was certainly different.

After checking the bag I got it from, I realised that it was from a new batch of the same clay that I'd received recently.

"Oh gosh...bother I said!!". Perhaps I even said a few other words that I'm not going to mention.

Lots of things went through my mind. The main one being "what if the two different coloured clays had differing shrinkage rates when fired? Will they pull apart? Will the sides and the bottom be a different colour? I'd just spent a couple of hours making and completing this pot, and I certainly wasn't going to smash it up just at a whim.

I pushed together all the scraps of left over clay and this is what I found. Certainly a different colour.

I wedged it all up and used it for another small pot.

Back to the original pot. I decided to bisque fire problems there although a slight
difference in colour remained. I took a risk and continued on and put it through a glaze firing. And guess what, it turned out perfectly!! I'm not really sure what happened with that particular bag of clay, but having checked the remaining bags, they all seem fine.

Lesson learnt....................always construct and complete a pot out of the same bag of clay?

Out of all the bags of clay that I've used, I've never come across this before, hopefully it wont happen again, but its something to be aware of. Clay is dug from different areas and its composition may be just a little different. That's my explanation anyway.

Happy potting.