Temperature accuracy

[Zeldazog]

Hi

Hope somebody here can advise.

I know that over time, kilns become less accurate.  I've had mine since October, and it hasn't been used that many times.

I usually do a full fuse at 804 deg C with a hold of about ten minutes (depending on the piece), using Bullseye.

I noticed a few firings ago that kiln wash had stuck to a couple of coasters, and a few pendants, taking it off the shelf.  But it didn't always happen.  I also noticed that sometimes there was a bit of needling to the edges, that I don't *think* was there before (can't be sure as I grind and re-fire a lot of work)  - but that again made me think I was perhaps firing a little too high, so I have reduced full fuse to 795 C now - and that has eliminated the needling.

I've just fused a plate in it, and its took most of the wash off the shelf - mainly in the pattern of the two coasters that were in there before.  They were on a second, but only a fire polish visit to the kiln.

It's not a major issue as I can just drop the temperatures accordingly, I knew it would happen at some point, but didn't it would be quite so soon.

Now, I think there's something else going on with the plate, as there is the biggest bubble formed it (from the underneath and right through the colour, not imbetween the colour and the clear top), so I don't think I cleaned the glass properly in the first place - real pity as it was lovely aventurine green!

I just wondered how long it is before the temperature reading can become inaccurate? 

I suppose the kiln could be overshooting as it goes through the second segment, which is a fast ramp from bubble soak to full fuse.  But I have been around when it has reached the top before, and never noticed it over by more than a degree or two.

[Lee - Kilncare]

A kiln shouldn't really behave much different, certainly over that amount of time.

As the elements tire it can take longer to heat up, which in turn leaves the glass in the heat longer, which in turn can give the appearance of higher temperature.

But this only counts when the kiln is full on as whilst it is firing at a given rate, the controller is turning it on and off anyway.

Voltage can also slow a kiln meaning if you used to get 240v in your house and your supplier has lowered it to 220 ish then that will give the same effect.

Certain thermocouple types can deteriate over time which will give a slightly different reading but not anything you would notice and certainly not so soon,

I can't answer your glassy issues mate but I don't think kiln "ageing" is your problem here, or it shouldn't be.

It may well be worth contacting the manufacturer to see if they can help. What kiln is it?

[Zeldazog]

Hi Lee

It's a Skutt Hotstart Pro - perhaps it has always run a little "hot", and I just never noticed before - a lot of the work I had done up to recently had all been reworked anyway, so I wouldn't have paid much attention to needling, etc.  And I had also sometimes used thinfire paper too, so kiln wash sticking wouldn't have been an issue.

Of course, there's a reasonably flexible range for fusing of glass, it doesn't just happen at an exact temperature and it will depend on the coloured glass itself too (like blacks soften earlier than whites, and so on) -

I can't say for sure that it is running too hot - I just remember reading somewhere that kilns do start to run a little hotter over time - trouble is, I have no idea where I read it!

I think first thing I need to do is scrub the shelf down completely and recoat it when I have time to do it properly for starters.  Then I will keep an eye on things.

I have been a bit naughty really because I havent' kept proper firing logs, to if I am perfectly honest, I don't know if there has been much of a change overall.  Slap my wrists.