PMC SPECIFIC kiln firing advice please....

Hello all,

I have a small enamel Hehlig front loading kiln which I bought as I specifically wanted to work with copper metal clay and wanted top quality solidly sintered results rather than using stove top methods etc. i also will use silver eventually but have done all in copper so far.

My max temperature according to the sticker on the kiln back and info I can find is about 940/960 degrees. So caution when I do work with silver as that is pretty much it’s melting point but no worries for copper. The kiln only has a dial numbered 1 to 10 for heat settings.

I did a lot of research and firing advice seems to be reducible to longer = stronger. I set my kiln at 4 for 20 minutes to ramp it then up to 8.5 for 1hr30, then turned off and let it cool for about 20 minutes.

I did my test firings like this and was very happy indeed with the results. Slim rods didn’t bend, all good and strong. Fired two more batches of copper items and again very pleased.

My issue is my electricity bill...!!!

After recovering from the shock I thought maybe I could cut down the length of firing time. Maybe ramp for 10/15 minutes then 8.5 or 9 for 45, so cutting my firing time in half. I will experiment, but I had it so perfect already :) ! So firstly, If anyone has any perspective and experience on this it would be most welcome.

Secondly, my significant other suggested a gas kiln instead of electricity. After a brief search online it seems to me that there is no such thing as a small gas kiln - they seem to be pretty big and ceramic orientated, which is different temperatures and a whole different world. It seems to me there is are reasons why jewellery making is with little electric kilns, if we could use small or even medium gas ones surely they would be out there? Am I missing something to do with temperature and controllability? Any information very welcome on this.

So hoping to hear some useful advice from those with more knowledge than me, in the interim will keep researching.

Alex.

In south Australia we have the most expensive electricity in the world, gas kilns will introduce other complications such as impurities in the gas, plus Oxidisation etc. when firing ceramics this is taken into account, plus it is more complicated to regulate the temperature, and tiny items may get blown about (remember there is a flame roaring about inside)and they need to be vented so extra fire precautions need to observed.
Try to do you work in batches to reduce the time the kiln is on.
I do not know of any manufacturer making small gas kilns you could make you own or have one custom made

That seems unusual for a kiln to have ramped up your electricity bill. Not sure where you are and I'm not familiar with your kiln but when I use my Paragon kiln for firing silver and bronze metal clay I never notice a major difference in my electricity bill. Does it have to have a dedicated wiring or do you just plug it in to any socket?

I looked into making one but it does seem that gas and temperature control is a thing, which is why they seem to come so big and primarily for ceramics. It did seem awfully complex and if no one else is doing it, then there must be a pretty good set of reasons. I feel no urge to pioneer! :)

i do load up each firing with as many as I can fit in without affecting the end result. It does plug straight into the mains, doesn’t run on three phase or anything like that. Maybe because it is old, I got it second hand from someone that used it for enamelling about 7 years ago but never had time to use it until now (lockdown has some benefits!) Maybe it just isn’t efficient any more. I am not that technical so don’t know if that is a thing.

I went for what is essentially just under a two hour firing after reading a lot, particularly Gordon K. Uyehara‘s approach. He uses Prometheus copper, AND uses carbon firing for it at about two hours. The manufacturers say carbon not recommended and 30 mins is fine for this brand, but his level of professionalism and proficiency is so high I figured to try to hit the same end product standard. After all, he had already done all the experimenting!

I did see a new Prometheus available with pre sets for each different type of clays - but I also read someone review that said each setting needed a lot of tweaking. Sadly, they didn’t go into what and why and there is no way of asking them where it was posted. Misspond, Is yours this one or one of the others?

In lieu of any other info I think what I am going to try is a pre firing gas hand held firing to burn off the binder then a second shorter firing of about 45 mins at a high temp (8/9 on my dial). I remember as a kid the used to be times of day that electricity was cheaper, I don’t know if it is still like that but I should probably find out! I am in Scotland.

Yes, it could be that your kiln is not running very efficiently. I've got a Prometheus Pro-1 that you set the run times for depending on what clay you're using and then the programmer stores those settings.

I've not used copper clay but do sometimes play with bronze clay and it's my understanding that the base clays such as copper and bronze both need to burn out, then be submerged in carbon in a suitable container as this reduces the oxidation that occurs as the clay sinters - you might find that doing the burn out with a torch helps but you do run the risk of over oxidising your clay at that stage with a torch.

I can't remember off hand how long bronze is fired for but have a feeling that after the 20 mins burn out its a 2 hour firing. And I do all of my silver clay for 2 hours too just to make sure it's properly sintered.

Something that comes up a lot in the Facebook metal clay forums is that people use the shorter firing times that the manufacturers suggest and their firings fail - the wisdom of those with experience is to ignore those shorter firing times and go for the longer option.

My kiln was second hand, like I say I don't notice that my electricity bill increases significantly so I'm not sure what else to suggest.