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Color Processing and the Thermal Profile of the SP-8x10

Tim Gilbert

People have been asking about using the SP-8x10 for color processing. The real question is: "how do you control the temperature?"

So we ran a thermal profile of the tray. The procedure is pretty simple:

  1. Fill the tray with water at the desired temperature and presoak for 1 minute.
  2. Empty and refill with water at the desired processing temperature.

We mounted a digital thermometer probe inside the tray and recorded the temperature over a 30 minute period.


You can see the results below (click the image to open the pdf):


As expected, the temperature dropped over time but not by very much (0C, 3.2C and 7C over 30 minutes). Frankly, we weren't surprised by the small heat loss. It's one of the reasons we made the tray of such heavy plastic (over 3mm thick). The alloy of ABS and Polycarbonate is a pretty good insulator; especially when compared to stainless steel tanks or some of the thin plastic ones.

Back to processing film, what you really care about is the average temperature over the processing time.

Note: contrary to what you may have been taught, it's the average temperature and not the absolute temperature that is important. Don't believe us? Just look at the instructions for any of the modern color chemistries: they list numerous time/temperature combinations. You can change the time to adjust for a change in temperature.

So when we process color film, we start with the chemistry just a few degrees higher (based on the ambient temperature and the expected processing time).

As a reference point, we show the "10 minute average" above but your results may vary so you should run your own tests. It only takes a few minutes and will save you the hassle of trying to keep the tray in a water bath.

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