Tray heater recommendations

[Terryro]

Does anyone have a recommendation for a tray heating mat? I've recently retired and downsized but I still like to make lith prints with my collection of outdated papers. I started in photography in 1974 after I enrolled in a college elective course and fell for the darkroom magic. I also have a lot of analog equipment which I'm downsizing as well. Send a message if seriously interested. Thanks for the help

 

[gijsbert]

I use a seedling heating mat, one of these https://www.amazon.ca/dp/B08F7NJ4JS , it's out of stock but amazon shows lots of alternatives.
I make my lith developer with warm water at about 35C and with the heat mat it stabilizes around 27-28C. It's low wattish, not too hot, doesn't melt my trays, I've left it on by accident a few times, no problem.
I've been looking for something that could keep a bit higher because I still have pretty long development times. I'm considering a food warming mat like this https://www.amazon.ca/dp/B0D6JZTXC8 but i'm very limited on space so it wouldn't quite work.
The lith printing group at facebook is fairly active, might be a good place to ask.

 

[DREW WILEY]

If atop a table surface and not themselves at risk of being under water, old Salton hot trays work quite well. Those were used to keep tV tray meal etc warm, and are both cheap and common on EBay.

 

[Nicholas Lindan]

The heating mats work better if they are well insulated from the bench. Place the heating mat on a sheet of Styrofoam and put the tray of pre-heated developer on top of the mat. Try it with water first to see what temperature the whole thing stabilizes at.

 

[Terryro]

Thanks for the recommendations. Much appreciated

 

[mshchem]

The heating mats work better if they are well insulated from the bench. Place the heating mat on a sheet of Styrofoam and put the tray of pre-heated developer on top of the mat. Try it with water first to see what temperature the whole thing stabilizes at.

 

[Beevo]

Does anyone have a recommendation for a tray heating mat? I've recently retired and downsized but I still like to make lith prints with my collection of outdated papers. I started in photography in 1974 after I enrolled in a college elective course and fell for the darkroom magic. I also have a lot of analog equipment which I'm downsizing as well. Send a message if seriously interested. Thanks for the help

I got one of these recently:

https://www.amazon.com/Food-Warming-Mat-Electric-Tray/dp/B0DK144621/ref=sr_1_4?dib=eyJ2IjoiMSJ9.tf55kVmhyNLCY021DNN_jzwk6PKlhpDdeRHanEAUYegJBMBd7ALNahKFK26qhZEap24z0y8u2VZaFggYeO8AkrvBmovKcWW1cndYf9xaM7bOnjavrRS2G0NG3JarAVJIrlbSVeMwDU4vZVuUSWYJfwmUypcA7iUeb6xcl1HxhGlZyBFcJKLp2OkeNhnukm-8dfOsLs-Ru0FXjFRFDiDQd656ayAs7hYWblUoNQeBpqE.cLAmoYw2_seCYD1m6Nw2MwZvyeib8Q6-zTdtbYV0F88&dib_tag=se&hvadid=695505661604&hvdev=c&hvexpln=67&hvlocphy=9030088&hvnetw=g&hvocijid=12313776833275615669--&hvqmt=e&hvrand=12313776833275615669&hvtargid=kwd-2266470953737&hydadcr=13933_13379050&keywords=food%2Bwarming%2Bmatt&mcid=95f55020ad7e36e7b1385d1ee20139a8&qid=1749494683&sr=8-4&th=1

I have not used it yet on chemistry, but testing with trays with water seems to work. I find that smooth bottom trays like Cescolite heat faster and better than the ones with a ribbed bottom.

 

[koraks]

I got one of these recently:

From the description:

3 adjustable temperature levels (140-212℉/60-100℃)

That's generally way too hot for most darkroom work with the possible exception of offgassing carbon printing gelatin 'glop', which could be done at the lowest temperature setting.
Now, a tray of water will dampen the temperature response somewhat so at least the heating of they contents of the tray will be slowed down; the larger total surface (walls of the tray, surface of the liquid) may in fact result in thermal equilibrium being reached at a lower point than the temperature setting on the mat. This depends mostly on whether the temperature control is thermostatic (good news: it likely isn't as this would add $0.10 to the bill of materials) and the actual power this mat works at. However...since the mat is designed to keep pots of food at a 60-100C temperature, which is a similar thermal profile to a photographic processing tray (similar liquid volume, roughly similar geometric parameters), the expectation is that your tray contents will drift up in temperature until they reach more or less the temperature set on the mat.

testing with trays with water seems to work.

How long did you test for, and did you start out with cold water in the trays or warm? If you intend to use this to gently heat up the liquid in a tray, then it'll work. It'll also work for lith development where the developer spends only a limited amount of time in the tray before it's being dumped or at least removed from the tray again (assuming one-shot development with a developing time up to ca. 15 minutes).

 

[Beevo]

From the description:

That's generally way too hot for most darkroom work with the possible exception of offgassing carbon printing gelatin 'glop', which could be done at the lowest temperature setting.
Now, a tray of water will dampen the temperature response somewhat so at least the heating of they contents of the tray will be slowed down; the larger total surface (walls of the tray, surface of the liquid) may in fact result in thermal equilibrium being reached at a lower point than the temperature setting on the mat. This depends mostly on whether the temperature control is thermostatic (good news: it likely isn't as this would add $0.10 to the bill of materials) and the actual power this mat works at. However...since the mat is designed to keep pots of food at a 60-100C temperature, which is a similar thermal profile to a photographic processing tray (similar liquid volume, roughly similar geometric parameters), the expectation is that your tray contents will drift up in temperature until they reach more or less the temperature set on the mat.


How long did you test for, and did you start out with cold water in the trays or warm? If you intend to use this to gently heat up the liquid in a tray, then it'll work. It'll also work for lith development where the developer spends only a limited amount of time in the tray before it's being dumped or at least removed from the tray again (assuming one-shot development with a developing time up to ca. 15 minutes).

I started with ambient temperature water. I set the mat to 158F and the water in the tray reached 101F after an hour and a half.

As an aside IMHO, the only way this would work for food warming is for hot plates of food to be placed on the mat

 

[koraks]

As an aside IMHO, the only way this would work for food warming is for hot plates of food to be placed on the mat

That's its intended purpose.

 

[mshchem]

My Dad used the seedling mats, he put them under a shallow (maybe an inch) sand layer in a tray. He used for keeping seed pots warm for germination. Worked forever. This was 35-40 years ago. It was magical to see how well it worked.

 

[Beevo]

My Dad used the seedling mats, he put them under a shallow (maybe an inch) sand layer in a tray. He used for keeping seed pots warm for germination. Worked forever. This was 35-40 years ago. It was magical to see how well it worked.

I have some and thought about those, but the lack of a temperature control had me look elsewhere.

 

[mshchem]

I have some and thought about those, but the lack of a temperature control had me look elsewhere.

Yeah, I think these held somewhere around 85°F maybe a bit warmer in a 65°F ambient. And now that you mention it there was some sort of a limit thermistor but IIRC no real adjustable control.

 

[Dennis S]

I use a tray heating mat and I also have wrap that keeps pipes from freezing and duct taped to ceramic tray and when both on I seldom get a temp more than 30C which works well for me on for Lith printing. There is just not enough darkness these days to do too much but collecting negatives to use next winter.

 

[AERO]

I have some and thought about those, but the lack of a temperature control had me look elsewhere.

Available on the Chinese seller AliExpress....(GOOGLE...)

3 Sizes ---Seedling Heat Mat Waterproof Heat Pad with 20℃-45℃ Digital Thermostat Controller Hydroponic Seedling Germination/
(Various sizes available)

 

[Beevo]

OK, I did a test of the food heater. 11x14

From the description:

That's generally way too hot for most darkroom work with the possible exception of offgassing carbon printing gelatin 'glop', which could be done at the lowest temperature setting.
Now, a tray of water will dampen the temperature response somewhat so at least the heating of they contents of the tray will be slowed down; the larger total surface (walls of the tray, surface of the liquid) may in fact result in thermal equilibrium being reached at a lower point than the temperature setting on the mat. This depends mostly on whether the temperature control is thermostatic (good news: it likely isn't as this would add $0.10 to the bill of materials) and the actual power this mat works at. However...since the mat is designed to keep pots of food at a 60-100C temperature, which is a similar thermal profile to a photographic processing tray (similar liquid volume, roughly similar geometric parameters), the expectation is that your tray contents will drift up in temperature until they reach more or less the temperature set on the mat.


How long did you test for, and did you start out with cold water in the trays or warm? If you intend to use this to gently heat up the liquid in a tray, then it'll work. It'll also work for lith development where the developer spends only a limited amount of time in the tray before it's being dumped or at least removed from the tray again (assuming one-shot development with a developing time up to ca. 15 minutes).

OK, I placed a 11x14 tray with 2L of room temperature water on the mat and set the mat to 212F. I placed one of my Onset Hobo data loggers in a small Schaller box to keep it dry and dangled the sensor bead in the water in such a way as to prevent it from touching the bottom of the tray.