Cromartie Hobby 20 kiln control switch

Let's get the most obvious one out of the way - are you using the small size cone? This is the size that is used for a cone sitter for our kilns (US). The larger ones will not bend when needed. It is unlikely you are making this mistake but one has to ask. You should also be using the large cones on your shelf to double check what temperature the kiln is reaching in different locations. You can either get wires to hold these up, get self supporting ones (more expensive) or simply mold a clay base. Easy to do - ask if you don't know how. I know Marianne has said that cones are not used in Europe to monitor heat work but from what I can see of your kiln, since it appears entirely manual other that the shutoff switch. You really have to know what temperature your kiln is firing to and eliminate that as an issue. I don't know what a .3 cone is. I only know of cones going from 022 to 12. 022 being the lowest temperature (heat work actually) and 12 being the highest. What temperature are you trying to fire to? If your .3 is our 03 then you should have certainly reached 1086C in 17 hours - What did your items sound like when they came out? Had the clay vitrified? What color was it? Knowing more from you would help. Donna

Hi Donna

Thank you for your reply. I now realise that when I referred to cones of .3 and .5 I should have said 03 and 05 as you guessed.

Today I visited the shop that sells pottery supplies and found that they had a spare control switch in stock. I bought it to save a possible second journey and having fitted it the kiln is now heating up at the lower settings whereas it wasn't before. I hope that I have solved the problem but if not I will post again.

You asked if the clay had vitrified but at the risk of displaying the extent of my ignorance I have to admit that I don't know. The outside of the bisque looked porous (and absorbed glaze hand painted on to it) but was relatively hard. Should it have looked and felt like glass?

Thank you for your help.

Peter

When you said you had fired for 17 hours but the the kiln sitter had not dropped, I was concerned that it was a problem with the sitter - had you fired that long and at high you should have gone past cone 6 even if you had done a slow ramp up. Since you did not mention a pool of glaze on your shelf where the pot had been, I assumed that you didn't over fire to that extreme of a degree. If you tap on the pot and it pings like glass then the clay has vitrified - that is it has heated to the point that you have formed glass within the clay body. That would tell you that you did indeed reach the temperature that the clay body you are working with matures to. The closer to greenware the more clunky the sound - the closer to maturity the more ping. At 03 the clay will still be porous but less so than 06 or 05 (what I bisque to). You should not be able to scratch the pot with your nail and it should have changed color if it has any iron in it (iron bearing clay will go from brown to peachy pink - to light pink to tan white (tan white is overfired for bisque). White will go from grey to white with the bisque looking much like the finished glazeware. It should not feel like glass. If you stick your tongue to it, it should absorb the water from your tongue rather rapidly but less so than bone dry greenware. The higher fire the less absorbant it will be.

I was trying to learn if you had overfired or underfired. It sounds however as if you have things more under control than you think. Marianne should drop in sometime. She is closer to your neck of the woods and might know more about your kiln. Let us know how things go.

Donna

When I next fire up the kiln I will check for "ping". The first pots I made did sound a bit clunky when I tapped on them but I didn't know how they should have sounded. As my wife kindly gave them away to her sister I can't now check them. No doubt I will hear if they fall to pieces.

Thank you again for your advice.