I am looking at buying a second hand kiln on eBay. I have found several. The insides all seen to have black/green stuff. For those who have kilns, is this just normal signs of use? Will this interfere with how well it works?
(I will try and include photos. If they upload, are there any that you think I should steer clear? Number 2 and 4 are open bidding at £0.99. 1 and 3 are £100 each)