Mug discolouration in conventional fan oven - any suggestions for a remedy?

[TeeDeeCee]

Hi,

I was wondering if someone might be able to help me with this: I'm cooking mugs in a domestic fan oven using clamps bought from TTP. Temps and timings are 17.5 minutes at 200 degrees C (being what I considered to be the minimum to get the blacks fully saturated) then cooling directly in lukewarm water (after feeling that fan cooling was worsening the condition I'm about to describe). On cooling, although the image is absolutely spot on, I find that the unclamped, uncovered area around the handle (and possibly even the handle itself) is discoloured. I've attached an image that shows a typical pattern with an obvious line caused at one edge of the clamp (1) plus the area covered by the tape (2). The area under the clamp is what I consider to be white (as it should be) which in the image merges seamlessly into the discoloured area (although that also often has a line at the clamp edge). As I said previously, fan cooling (though with probably not enough airflow) seems to make it worse. If I reduce the cooking time by very much, the blacks start to become a bit temperamental. The mugs are 10 oz, ceramic, Durham mugs bought from Mega Electronics along with a mug press (in which they seemed to perform well but which I want to move away from). I feel like I'm chasing my tail a bit now so any suggestions as to possible causes (although I appreciate it's proabably heat related) and remedies would be very gratefully accepted.

Thanks in anticipation

Scott

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[pisquee]

Is this a new oven that you are only using for making mugs, or is it a used oven, or one you are also using for your cooking?

[TeeDeeCee]

Thanks for the reply. It's our home oven.

[pisquee]

If it's domestic oven which is still used for cooking, then I assume it isn't pristine clean, and that there will be residue from food cooking which could explain why your mugs are taking on colour in areas where they are not covered up.
You need a separate oven for mug printing - a (new and clean!) domestic size oven if you're planning on doing a lot of mugs at a time, or a smaller one if not - also, I don't think the fumes from your mug printing will do much good to your food either.

[TeeDeeCee]

That is a very fair point and makes sense - I wish I'd thought of it. I was intending to purchase an oven specifically for the purpose and will give it some priority. It probably means it's time to clean our oven though (embarrassing)! Thanks a lot for your help, it's much appreciated.

[SciArtImages]

I use a halogen oven (dedicated to mugs) and have had this problem. I assumed it was because of a little bit of gassed ink getting into the air, and because of the confined space stayed around and when it hit the mug (at sublimatable temp) it did it's job.
Anyway, the way round it (I found) was to cut the print-out larger (so the paper is slightly taller than the mug and longer such that you have to slightly 'break' the ends of the paper over the handles if you see what I mean). This virtually covers the whole mug and hey presto, no more problems.
Hope this helps.

Neil.

[Renniwano]

I agree.. that looks like blowout to be honest and can happen in a dedicated mug oven too

[TeeDeeCee]

Your advice is much appreciated - thanks very much everyone.

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If the markings are due to grime from also using the oven for cooking, then I would expect to a degree to be able to wash/bleach it off (although it may be pretty baked into the coating of the mug) If it is gases from the ink (which I do agree that it does look like) then no amount of washing is going to remove it.
Either way, you need a separate oven for sublimation work!

[TeeDeeCee]

Yeah, it's absolutely locked in.