Mercury thermometer recommendation?

[Radost]

Depends on what you mean by color photography. Making consistently matched color separations via black and white film might ideally demand tolerances within plus or minus 1/10th F. I actually have a thermoregulator capable of that kind of accuracy. But I rarely need it. And it in turn needs to be calibrated using a truly trustworthy, accurate thermometer, not some cheap toy thing.

Ordinary RA4 processing, just like Cibachrome of the past, can easily tolerate plus or minus 3 degrees, though I have always kept it tighter than that. With routine black and white film developing, I just use one of those Zone VI compensating developing timers with its water jacket probe. As long as I start out a little above 20C, any drift down in water temp seems to be correctly factored in.

I mean C41

 

[Philippe-Georges]

Mercury thermometers may no more be sold in the EEC due environmental regulations...

Mercury is highly toxic and does not degrade in the environment, when it gets in the water/river it destroys aquatic life and can not be stopped doing so.

 

[Agulliver]

It's still possible to buy mercury thermometers for specialised applications. I bought three in 2021, 0-400C mercury thermometers for laboratory use. But these are only legally sold to laboratories and schools. You can't buy one as a member of the public.

the toxicity of mercury to humans is often exaggerated, though it certainly is toxic. Several early European chemists and of course hat makers famously suffered mercury poisoning. These people used to ingest the mercury orally over many years, indeed Lavoisier was said to be a mercury addict. However, you're not going to do yourself any harm with a thermometer...the biggest risk is breaking the glass and cutting yourself. It's more toxic to aquatic life, so the biggest issue is correct disposal of broken mercury thermometers. Also if you were to be silly and collect the mercury from a few dozen thermometers and then sit it in an open container and let the vapours go into a room....that might cause mercury poisoning.

A good mercury thermometer is far less prone to the liquid strand breaking than the modern low toxicity spirit thermometers, but in almost all practical terms both are as good as each other at measuring temperature. Certainly at film processing temperatures.

Form my POV that just means I have to replace more thermometers each year than when we used mercury because school kids tend to drop them. The glass rarely breaks but the strands in the spirit thermometers are prone to breaking. Sometimes it's possible by heating or freezing to reconnect the strand....but often it's just easier to replace the thermometers.


If OP is able to buy a mercury thermometer, any functional example will be reliable. But unless you can calibrate it you don't know how accurate it is. Alternatively, experimentation can determine what reading on your thermometer corresponds with good C41 development. If you go the spirit thermometer route, buy several at once and calibrate them or at least note what they all read at the "right" temperature. They may well be slightly different. Then if you do find one suffers a broken strand, you've got backups with known calibration.

For electronic thermometers, I recently bought 15 for student use. And I can tell you, even a middle of the range device....all 15 read slightly differently. They have calibration screws but for that you'd need a super accurate 0C and 85C or 100C heat source. It's part of how we teach the kids about accuracy vs repeatability and calibration of instruments.

 

[Donald Qualls]

What do you test it on, and how?

For thermometers a range that includes 0C, the triple point of water (where pure water boils and freezes at the same temperature, ~0.1C at some tiny pressure, as I recall) is the classic calibration point. There are other triple points that can be used to calibrate at other temperatures as well. Triple points are used because they can be reproduced anywhere, any time, with pretty simple equipment -- and because they include their own pressure as well as temperature, they'll always be the same for any given pure material.

Obviously, you don't adjust the thermometer or its scale, you just make a note to keep with the instrument detailing how much high or low it reads at what temperature (just as you'd do after a CLA of an old leaf shutter).

 

[Radost]

Calibration of a mercury thermometer is impossible.
The way to test is is to put ice cubes in a glass and wait for it to melt a little.
Then start stirring the thermometer without touching the glass.
It should read 0c 32F.

 

[Patrick Robert James]

I have a Kodak color thermometer (not sure if it is mercury) and a bunch of dial thermometers. Every now and then I take out the Kodak and using that as the constant I check all the dial thermometers. Usually they are all super close. Good enough for black and white work. Never had an issue with color either but I scan that so it isn't as critical for me as someone who prints I suppose. At some point good enough is good enough. I guess we each have to decide at what point that is.

 

[titrisol]

Calibration of a mercury thermometer is impossible.
The way to test is is to put ice cubes in a glass and wait for it to melt a little.
Then start stirring the thermometer without touching the glass.
It should read 0c 32F.

Yes, (0.01C) and then note the "offset".
If it reads +.5 then you have to substract that from every reading.

Since photography uses the 20-40C range that 1 point calibration might be sufficient for an acceptable error.
If you want to be nitpicky is much better to use a thin neck flask (e.g erlenmeyer flask) and cover the top with plastic wrap or a rubber stopper to allow the pressure to equilibrate at +6.1mbar

 

[Radost]

I have a Kodak color thermometer (not sure if it is mercury) and a bunch of dial thermometers. Every now and then I take out the Kodak and using that as the constant I check all the dial thermometers. Usually they are all super close. Good enough for black and white work. Never had an issue with color either but I scan that so it isn't as critical for me as someone who prints I suppose. At some point good enough is good enough. I guess we each have to decide at what point that is.

I scan too. But developing in the right temp saves a lot of post work. I don’t like wasting time and doing post.

 

[nsd]

Anybody has a Mercury thermometer recommendation and where to source it?
I purchased a thermoworks one but I feel it got a little off with time.
I simple mercury thermometer with give me the most consistent and accurate reading.

Perhaps check with reproducible measurements? Ice water should read 0C and boiling water at sea level (to be exact, at average sea level atmospheric pressure) 100C. Then you'd know if the thermoworks did drift. And some (the fancier models) are adjustable.

 

[Steven Lee]

@Radost I've had this bookmark saved for a while, but haven't pulled the trigger yet. I hope this helps!

 

[DREW WILEY]

There was once a warehouse within walking distance of my work place which dealt strictly in thermometers. There were all kinds of pharmaceutical and biotech labs in proximity, and UC Berkeley right up the street. Thousands of kinds of thermometer. And Lawrence Berkeley Lab up the hill has "thermometers" which read within millionths of a degree. Of course, they have a little bigger budget than you or me. Just sayin'. You get what you pay for. Take a look at a catalog or website from any serious lab supply company like LSS, and you'll find true certified scientific glass thermometers of a similar price category to what Kodak Process thermometers once sold for.

But that boiling water test? Ha! Any of us who have done a degree of mountaineering know that when water begins to boil at 10,000 ft it's still so lukewarm you can put your finger into it without getting hurt. A "rolling boil" is necessary to cook your freeze-dried dinner or whatever. To calibrate a thermometer relative to that standard, one has to factor in a number of variables not only including what "sea-level" actually means, but ambient barometric pressure as well.

 

[xkaes]

But that boiling water test? Ha! Any of us who have done a degree of mountaineering know that when water begins to boil at 10,000 ft it's still so lukewarm you can put your finger into it without getting hurt. A "rolling boil" is necessary to cook your freeze-dried dinner or whatever. To calibrate a thermometer relative to that standard, one has to factor in a number of variables not only including what "sea-level" actually means, but ambient barometric pressure as well.

I wonder if Speke was this concerned about his thermometer's accuracy when he used it to determine the altitude of Lake Victoria -- and claimed it as the source of the Nile.

 

[DREW WILEY]

Even the level of Lk Victoria no doubt fluctuates seasonally, so it wouldn't make much difference anyway. That's what surveyors and transits were for; but first a lot of reference point had to be climbed on clear days. Try the boil test on the altitude level of Lake Mead at the moment. Not only is it nearly dry, but probably the mineral or salt content has risen enough to alter the boiling temp of water behind the dam, not to mention the air temp itself being hotter than hell in summer.

 

[Paul Howell]

I have had my Kodak process thermometer for 55 years and I got it used, I've used it for C22, C41, R4 and what R4 replaced, E4, E6, and GAF/Anscochrome and color negative chemistry. As it is sealed and mercury does not react with glass, never worried about a false reading, negatives and slides are spot on. My thinking is that temperature fluctuations are more of a concern than being a degree off as long I am off a constant degree every time and my times are fixed. For ease of viewing I use a dial type, a Patterson I think, I use my Kodak to keep it calibrated. I expect that a good certified digital thermometer will be as accurate.

 

[Radost]

I have had my Kodak process thermometer for 55 years and I got it used, I've used it for C22, C41, R4 and what R4 replaced, E4, E6, and GAF/Anscochrome and color negative chemistry. As it is sealed and mercury does not react with glass, never worried about a false reading, negatives and slides are spot on. My thinking is that temperature fluctuations are more of a concern than being a degree off as long I am off a constant degree every time and my times are fixed. For ease of viewing I use a dial type, a Patterson I think, I use my Kodak to keep it calibrated. I expect that a good certified digital thermometer will be as accurate.

I have a thermaOne and am waiting for 2 kodak color
will test

 

[Paul Howell]

I found that have another mercury thermometer, an Simmon Omega, stirring rod Photo Lab scaled from 30 to 140 F. I just put both (Kodak and Omega) in tap water, our tap water this time of year is already warm, both read 84 degrees, looking very close might less that a degree difference. Then I checked my dial type a Tell-True untiliy, it read 83 so I adjusted it to 84.

 

[BobUK]

For the sake of completeness, I must mention the mercury plant that was at ICI Runcorn. Not sure if it is still there now.
A chap that worked there all his working life was five foot eight inches tall but, on a hot day he was six foot two.

 

[DREW WILEY]

Lots and lots of mercury is still being mined somewhere or other. Its a key ingredient in fluorescent light tubes, and in many electronics and military applications. Getting mercury scientific thermometers is easy if you know the right sources. People aren't supposed to eat certain species resident to SF Bay here due to all the "quicksilver" mercury contamination which came down the rivers from way back in the Gold Rush era. It was mined near the south end of the Bay, and native Americans used that red cinnabar to paint themselves and their utensils.

 

[Brendan Quirk]

I was given an expensive digital thermometer by a lab chemist. The instruction leaflet said it would be guaranteed accurate for two years. After around eighteen months it was way out, useless, even with new batteries.

So how do you know your mercury is faulty and it is not the digital?

What do you test it on, and how?

The only spirit thermometer that I use is small five inch one kept in the corner of the print developer dish.
Spirit is good enough for my printing.


An interesting short article link to darkroom thermometers.

I do not know about your digital thermometer, but generally they are based on the thermocouple. A thermocouple is a pair of wires of different compositions, which, when twisted together at one end, produce a voltage at the other (not twisted) end. This can be read by a voltmeter, chart recorder, etc. This voltage is proportional to temperature at the thermocouple. Tables of voltage vs. temperature have been accurately and precisely determined since long ago.

Basically, a digital thermometer is a voltmeter calibrated to read out in degrees (F or C or whatever). "Back in the day" we used to measure voltage directly and read the temperature off of the appropriate chart. Some may remember the "J" chart.

Thermocouple wires had "names"; the J type was iron-constantan ( I don't remember what this alloy was.) Another popular one was type K. Dial thermometers use the same principle; the dial replaces the voltmeter.

All this is really just for info. The voltage generated by the thermocouple should be stable, and not drift with time. I can not say about the voltmeter, although I never heard of one drifting. For the perfectionist physical chemist, I believe there might be slight corrections necessary, such as for how much of the thermocouple is immersed, and how much is not.

 

[Brendan Quirk]

A few of my mercury thermometers have engraved on the back "76mm immersion" etc.
One reads "total immersion"

Apart from me, does anyone take any notice of these instructions.

This was for very precise measurements in physical chemistry. we are talking small fractions of a degree. Just don't immerse the whole thermometer!

 

[Brendan Quirk]

Mercury thermometers may no more be sold in the EEC due environmental regulations...

Mercury is highly toxic and does not degrade in the environment, when it gets in the water/river it destroys aquatic life and can not be stopped doing so.

Mercury is not acutely toxic, but is so with chronic exposure.

PS. Mercury is converted to methyl mercury in the environment I believe, which is way worse!

 

[Chan Tran]

Calibration of a mercury thermometer is impossible.
The way to test is is to put ice cubes in a glass and wait for it to melt a little.
Then start stirring the thermometer without touching the glass.
It should read 0c 32F.

water freezing point and boiling point can't be use with the Kodak Process Thermometer type 3 as it only read from 55F to 140F.

 

[Radost]

I do not know about your digital thermometer, but generally they are based on the thermocouple. A thermocouple is a pair of wires of different compositions, which, when twisted together at one end, produce a voltage at the other (not twisted) end. This can be read by a voltmeter, chart recorder, etc. This voltage is proportional to temperature at the thermocouple. Tables of voltage vs. temperature have been accurately and precisely determined since long ago.

Basically, a digital thermometer is a voltmeter calibrated to read out in degrees (F or C or whatever). "Back in the day" we used to measure voltage directly and read the temperature off of the appropriate chart. Some may remember the "J" chart.

Thermocouple wires had "names"; the J type was iron-constantan ( I don't remember what this alloy was.) Another popular one was type K. Dial thermometers use the same principle; the dial replaces the voltmeter.

All this is really just for info. The voltage generated by the thermocouple should be stable, and not drift with time. I can not say about the voltmeter, although I never heard of one drifting. For the perfectionist physical chemist, I believe there might be slight corrections necessary, such as for how much of the thermocouple is immersed, and how much is not.

water freezing point and boiling point can't be use with the Kodak Process Thermometer type 3 as it only read from 55F to 140F.

I have read some where that a drop on those can bang them out alignment And show different temperature

 

[DREW WILEY]

The cinnabar mercury from our old local mines converts to methyl mercury when tailings are washed downstream into the wetlands adjacent to the Bay, where that occurs. But much of the old gold mining mercury which has come far greater distances via the rivers arrives in the more hazardous form, or has already gotten into fish.

 

[ic-racer]

Fisher is having a blow out sale on calibrated mercury thermometers. This one is full immersion, so it is used to test your other thermometers.