Thermometer -

Barney

Barney

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Wayne
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How accurate is accurate enough for a thermometer used in developing?

I carried out a rudimentary test using a glass full of ice with water added, I ended up with a reading of 0.6 degrees. I appreciate that it wont get down to Zero as I am measuring a cold liquid at just above freezing temperature.

Is it near enough?
 
The issue with calibrating measurement devices such as these is that it is very difficult to know the temperature of the thing you are measuring well enough before the calibration commences. Just ask NPL. Measuring absolute temperature is very difficult. Measuring relative temperature is easier, but tells you less information. Let's not even get started on calibration drift over time.

Generally speaking I would suggest doing test developments and log the measured temperature of the thermometer you're using with the results achieved. Over development in relation to the results you want means the temperature is too high, and vice versa.

Alternatively, if you really want to know, buy a calibrated thermometer.

For B&W, a degree either way is not likely to yield much difference, for certain stages of slide development, issues can start to creep in around a few tenths of a degree out (from what I understand)
 
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Years ago - meaning the mid 1960s - Paterson sold two different certified thermometers. I think certified by the NPL, but I'd need to check. The mercury version was sold as certified to plus minus one fifth of a degree, for colour work. The spirit version had a wider range (possibly plus minus a half degree) for Black and white. The mercury was faster reacting.

I eventually got 3 of the mercury ones, in case one broke. They all agreed with each other, and I haven't yet broken one.

As Jonathan said, consistency matters more, but colour casts can be corrected (and introduced) with reversal film very easily with small changes.

I haven't checked colour processing chemistry, but as the Ago processor's selling point is that it monitors temperature and adjusts the time during processing, making colour simpler, it implies to me that temperature variation can be adjusted by time, and therefore the absolute temperature is not too critical.
 
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For processing black and white consistency is far more important than accuracy anything better than a degree is certainly good enough.
Time temperature and dilution and agitation, are all factors important to development. None of them are likely to be exact, what ever that might mean.

Errors in Any of those factors can lead to a negative that is over or under developed.
An Over or under developed negative alters contrast and graininess far more than it does density.
While over or under exposure alters density more than contrast.
Beginners find judging this from a processed negative quite difficult. But it comes with experience.

But back to your thermometer. Stick with one temperature. Probably 20c degrees 68f. If you need more contrast increase development time. Do not mess with the temperature if you can help it.. I use stainless tanks so temperature changes quite a lot during development, unless I keep them in a water bath.
Do not worry about the accuracy of the thermometer it will certainly be consistent.

Consistency is the key, keep agitation temperature, time and dilution the same, if you need to change anything only changed one of them, preferably the time.
 
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I found that, if I was within spitting distance of 20°, my negatives were adequate for my needs.

As an assistant, I was told to check all the thermometers every month, by putting them together in some warm water for five minutes, taking them out and writing down the readings. If they were within half a degree of each other all was well. They always were.
 
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