Developing Temperature Control

[Ian-Barber]

One of my biggest headaches when developing film is temperature control.

I have been allocated a small corner of the conservatory for my film developing. Being a conservatory, it can get very warm in the summer (37°C) and very cold in the winter (16°C). We do have a radiator but during the winter months we retire to the main living room which is heated with a log burner.

Summer
During the summer, I usually end up having to cool the developer down by standing it in a bucket of water or waiting until night time when the temperature falls to close to the working temperature.

Winter
During the winter, I have been using a 150watt aquarium heater in a plastic container filled with water to bring the temperature up to the working temperature.

This worked quite well when the total development time was short ( 7 - 12 minutes)

Aquarium Heater Issues
The aquarium heater thermostat works on a bi-metal strip which expands and contracts as the water temperature changes. Getting the water up to temperature wasn't to bad but the bi-metal strip was very slow to respond when the water temperature dropped. In fact, when set to say 20 degrees, the heater didn't turn back on until the water temperature dropped to 16 degrees.

Another issue I was finding was that I was getting hot/cold spots probably caused by the water not being circulated.

Aquarium Pump
I tried a small aquarium pump but this didn't seem to cure the issue with the bi-metal strip on the heater.

Why Worry
Since moving towards extended development times and minimal agitation with Pyrocat HD developer, there are instances when the total development time can be as long as 55 minutes where the film could be stood for 18 minutes resting.

To be consistent, I was concerned that during this extended time in winter, the developer could drop below what I was comfortable with knowing the slow response time from the aquarium heater thermostat.

Possible Solution - Sous Vide Cooker
After stumbling across a video I became interested in trying a Sous Vide Cooker which is supposed to accurate to +/- .1 degree so I ordered one to try. First impression is very good. The small water circulator constantly keeps the water moving preventing hot/cold spots.

My working temperature for Pyro is 70°F (21°C). After some testing, I found by setting the Sous cooker to 22° I could maintain a constant temperature of the chemicals with ease. I left it running for just over 2 hours and the temperature never moved.

 

[David M]

Good idea. And you can have gourmet meals when you're not processing, too. Moderately expensive, though.

 

[Ian-Barber]

Compared to the Nova processing unit, its quite cheap. Now the temperature in the conservatory is dropping its working a treat. As we speak I am processing an N+3 for 57 minutes and the temperature never moves from where I set it at 70°

 

[David M]

A very good point.
For cooling chemicals more quickly, I have some of those plastic brick things that are used in picnic boxes. There are small ones, about 2" square, that will float at the top of a measuring cylinder until the temperature has dropped. This works well for my short (6mins-ish) developing times.
If the room's ambient temperature is too high, I suppose you could float a couple of these in your water bath to cool it and then use the sous-vide device to counteract the cooling effect and bring the overall temperature back to what you want. I hope this makes sense. It's just popped into my head and I haven't worked it out fully. For long developing times, you might need to replace the bricks at half time.
I might have to visit Lakeland.