Expert: Sam Kelly - 8/13/2008

Question
This engobe I've been using for a few years from a single large batch is NOW in the NEW batch suddenly running. I am so disappointed and trying to figure out WHY?! Is is the darker clay with more iron? Did I mix up chemicals wrong? I'm still experimenting, even though I swore I never would again, as I'm of the school whatever happens happens. This old engobe I could put on thick and do scrafitto and then fire it and put my mason stains on and just do anything. It was wonderful.... The mason stains took on the shine of the engobe...Most recipes I see say the engobe is flat and needs another clear.... Not for me. This one is great... Or at least was. I'm going to remix it AGAIN, and try it on a lighter clay. I keep using different clays now too... and wonder if the Iron content is affecting it.... then I remember I did use it on a lighter colored clay. So many variables. WOrking in a community environment the way I do i'm wondering if someone may have put the chemicals in the wrong buckets... The person insists NO! But the frustration is keeping me coming back, but I did think I was past the experimentation stage and could concentrate on creating....
Any suggestions to STOP the engobe Dead in its cracks. This engobe even flowed at cone 3 when I use to take the old one to cone 6.... Any help would be appreciated... Thanks!

Answer
Hi Scott,
What a pain, I make all my own glazes and clay bodies so I sympathies.
A couple of things first, I have never seen an engobe go shiney in a firing as they are not glazes, and was the first batch you actually mixed an engobe?. There's nothing to say that the first batch made was true to recipe.
The only way we are going to be able to tackle this is to make a test batch from new materials sourced from a supplier. This will make sure what you have used wasn't contaminated. There are no short cuts and experience tells me this is what has to be done.
If you want to e-mail me the recipe or list it here I will make it up from available raw materials(I'm in Australia) I have and test it for you.
Use my contact form from my web site http://www.samkellystudio.com.au/contact.php