The temperatures in my house fluctuate wildly. I spend a fair amount of time before printing just bringing my chemistry to temperature. Are there any automated solutions or aids that help with this? I'm imagining an incubator rack where I can insert 4 1-liter bottles of solution and come back an hour later to find them all at 68F.
I just googled for 68 F hot box to see what came up and I was surprised to see that home brewing may also be your friend here.
From the first random link I saw 9 Devices That Can Heat or Cool Your Fermenter
When it comes to fermenting, temperature is one of the most important steps towards happy yeast.
Ale yeast is happiest at 68 to 72°F, while lagers usually perform best at 45 to 55°F.
I followed a link to Amazon from that article and found: Inkbird Pre-Wired Dual Stage Digital Temperature Controller Outlet Thermostat 110V, 1000W Heating and Cooling for Fermentation Kegerator ect which costs $35. Which could be the basis of a home built system for you.
So while I don't have a specific solution, looking at other hobbies that require temperature regulation will open up a bunch of different potential solutions.
Adjusting and keeping the chemicals of the process is a challenge faced by every amateur darkroom enthusiast. Best is a water bath. Procure a plastic pan large enough to hold the bottles. It wouldn’t hurt if there is room for the developing tank. You place the chemical bottles in the pan filled with water. The water level should be deep enough to half submerse the bottles. Now add hot water or ice to this water bath. The idea is to bring the solutions in the bottles to temperature. Once the temperature of the fluids are adjusted and checked, you can start the developing sequence. Load the film onto the reel in total darkness and place the film in a lightproof developing tank. During the developing phase, you park the developing tank in the water bath; this keeps the fluid inside spot-on.
Throughout this darkroom regimen, you regularly check temperatures. You can simply add hot water or ice to the water bath. If you will be doing this on a regular basis you can get more elaborate. You can install a thermostatic mixing valve on your incoming darkroom water line. These are expensive but worth the money. You will need a darkroom that has a working sink. You run tempered water into a pan that contains the bottles. Also, chemical laboratories frequently use a water bath. You can purchase an inexpensive electric water bath tray; check the web or find a chemical supply house. This tray uses a submersed electric water heater with a thermostat. Luckily, most color processes call for elevated fluid temperatures. This is no accident; setting the processing temperatures high avoids the need to refrigerate the solutions.
If you need to adjust a fluid temperature quickly, use a plastic baggie filled with ice or hot water. You dunk this into the fluid, the baggie method keeps the temperature adjusting fluid contained so the chemicals are not diluted.
They are pretty standard items in most labs... The problem is that they usually cost a fortune. Many of them have a hose and pump that allow you to circulate the cooling fluid (in your case, water) through some other apparatus or larger container. E-bay has some here. If you're into do-it-yourself, I'd suggest looking at thermoelectric coolers such as this. It can heat or cool contents depending on the polarity of the 12V power source. A cheap temperature controller such as this coupled with an 'H' bridge controller such as this or this. Some learning will be involved.
This is probably overkill for your application. A mixing valve like this might be better for you if you have a source of hot and cold water available and are willing to do some plumbing.
For black and white applications, such a device might be overkill. Film and paper develop over a range of time/temperatures combinations (unlike color applications where time and temperature are crucial). It might be best to adapt your workflow to ambient temperature. But a water bath will bring your chemicals to temperature quickly. For long print sessions, you might consider a solution like floating trays in a large water bath (like a large sink) if your work area will accommodate it.
For my black and white processing I use a large washing up bowl half full with water. A 100w aquarium heater/thermostat and a separate imersive digital thermometer for accuracy. Our darkroom setup is in the garden and can be quite cold at times. 20mins standing in the heated 20C water keeps the chemicals just fine. I stand the film container in there too between agitations. Once done, the water is reused to mix chemicals for the print trays. Works a treat. All available via Amazon for £25.
One option is exploring thermostats for aquariums:
I can not recommend a specific model or brand, but it is an idea.
As all electric gear, disconnect it before putting your fingers inside the water.