Thermometer -

Barney

Barney

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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.
 
StephenM said:
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.
Click to expand...

Breaking a mercury thermometer on to a silver based film could have interesting results, in theory at least the mercury could form an amalgam with any silver it contacted.
Never known it happen though. However mercury makes a mess of gold rings.
 
Pedant mode on/

I said "I hadn't broken one"

Pedant mode off/
 
I started developing colour prints in 1979 and the chemicals had to be used at 40C and held to within 1C. At first this was difficult but a company producing a tropical fish tank heater offered a modified version just for amateur photographers. They guaranteed it accurate to 0.5C. It was very successful so when the chemical company brought out a room temperature version, I continued with working at 40C as it was still the optimum and much faster. I did this for 20 years but then moved on to scanning the negatives until I bought a DSLR in 2005.

Dave
 
Thank you for all the tips, I got a new thermometer, one of those cooking types, and checked to my old one which is + or - 0.3 degrees, it was showing 0.1 colder so its not far off.

I started having runaway thoughts all day regarding accurate temperatures, thermal gradients if the warm water bath is not all the way up the developing tank or if the tank is placed on top of a cooler surface. Doh.

I agree that consistency is the key and I will try to keep my routine the same and then make any adjustments through manipulating the overall development time.

Thanks again !
 
For what it's worth I make up the developer to the correct temperature while stop and fix are reaching temperature in water in a washing up bowl. The tank only comes out for agitation and changing chemicals. The thermometer isn't used after the developer goes in, and I don't adjust my times.
 
StephenM said:
For what it's worth I make up the developer to the correct temperature while stop and fix are reaching temperature in water in a washing up bowl. The tank only comes out for agitation and changing chemicals. The thermometer isn't used after the developer goes in, and I don't adjust my times.
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Thanks Stephen, there are so many different methods that people are adopting, I did not keep my tank in the washing up bowl, just set it down in the bottom of the bath.
I think I will take a couple of readings through the development to see whats happening in my method. I suspect there will be a huge difference with regard to what is happening over winter and summer where ambient temperatures are not as consistent.
 
Barney said:
Thanks Stephen, there are so many different methods that people are adopting, I did not keep my tank in the washing up bowl, just set it down in the bottom of the bath.
I think I will take a couple of readings through the development to see whats happening in my method. I suspect there will be a huge difference with regard to what is happening over winter and summer where ambient temperatures are not as consistent.
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A water bath is good for consistency. Summer or winter, Some times it is preventing the tank heating up some times from cooling down

You do not need to have a film or developer in the tank to test temperatures over time.

Just fill with water and go though the motions take a reading before you start and at the end of the development time. Use your normal agitation methods.
Try it with and without a water bath.
If your room temperature is around the normal 18 to 22 degrees there will be little change anyway.
However if the average temperature range is around 20 degrees over the period there is nothing to worry about. Even if the temperature in the tank were to go from 18 to twenty two degrees the average would still be 20 degrees and it would result in correct development. This is because development is directly proportional to temperature over time.

Within reason the temperature of the fixer and washing water is far less important. however sharp changes in temperature can cause the emulsion to reticulate. This was common prior to the early 1960's but I have never seen it since. These days the gelatine is more stable. Colour film processing needs good temperature control at all stages.

When I had a professional dark room every thing was set to 20 degrees including the air temperature and washing water.which was also filtered.
 
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Terrywoodenpic said:
Within reason the temperature of the fixer and washing water is far less important. however sharp changes in temperature can cause the emulsion to reticulate. This was common prior to the early 1960's but I have never seen it since. These days the gelatine is more stable. Colour film processing needs good temperature control at all
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The only known time I had reticulation was a single film from 1965. I say "known" because less extreme examples than the one I had can be missed.
 
StephenM said:
The only known time I had reticulation was a single film from 1965. I say "known" because less extreme examples than the one I had can be missed.
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Mine was a single example from 1974. I still waste my time warming up the wash water, too!
 
Wash water temperature has an effect on wash times. See Grant Haist, vol 1. You can wash in  sewage sea water for the first stages as being slightly more effective. Apparently.
 
StephenM said:
Wash water temperature has an effect on wash times. See Grant Haist, vol 1. You can wash in  sewage sea water for the first stages as being slightly more effective. Apparently.
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Cruise photographers had limited fresh water and had little choice but use some filtered sea water. But it. Leaves a salt scum on film as it dries. So final washes must be in fresh water.
One way and another film photography uses a lot of water. Modern Colour processing and printing machines use remarkably little.
 
Terrywoodenpic said:
Cruise photographers had limited fresh water and had little choice but use some filtered sea water.
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I remember an article about cruise work in a photography magazine, probably in the early 1960s.

There was a bit in that about all the water being distilled on liners, so there was never a shortage. I suppose the systems used must have varied from ship to ship.
 
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