I Broke My Thermometer. Need Replacement

Well I broke a very longstanding promise tonight that I wasn't EVER going to let this thermometer get broken. It was about the 4th one I've owned in my 49 years of developing. my prized Kodak Color Thermometer, also called Kodak Darkroom Thermometer. The one that comes in the long round black tube, about 10 inches long, blue liquid, very accurate. And very fragile. It's gone. I don't want some ebay replacement--most of them are not accurate. I would have thought it would be easy to find some cheap Chinese digital one, because I'm tired of worrying about breaking glass thermometers. Besides, I can't buy one now anyway. It's August. The mailman would put it in the outdoor metal PO boxes, which are like an oven. It would explode sitting in there. I've already lost 2 glass thermometers that got too hot and broke. And I don't like dial thermometers, like the old Weston. They aren't accurate worth a toot. Ideas? Thank you.

Get a digital one at the grocery store. They're cheap and accurate.

I've never seen one at a grocery store.

Get a digital one at the grocery store. They're cheap and accurate.

+1 to 'Get a digital one'.

'Cheap and accurate', not so much.

 

I've got several 'cheap' digital thermometers, including two supposedly designed for laboratory use. None of them came 'accurate' out of the box. Typically a degree or so out.

 

Not really a problem as long as you know that it reads 0.8 degrees low at 20 C, or whatever. But to find out you either need another known calibrated thermometer, or to spend some time with crushed ice and water, and boiling distilled water baths. Not forgetting to make allowance for the current atmospheric pressure in your boiling-point calibration.

 

It might be easier in the long run to get a 'Brannan', or similar laboratory certified glass thermometer, against which to calibrate your cheap digital thermometer. Keeping the glass thermometer safe in its keeper and using the robust digital one for everyday use.

When I was processing lots of film on a regular basis I used to check my dial thermometers once a month against a Kodak color processing thermometer--a mercury thermometer in a heavy stainless steel casing. Unless I had dropped my dial thermometers (including a Weston) they stayed well within 1/2 degree F. and could be easily recalibrated. The community college where I teach has had mixed results with digital thermometers--they haven't been that accurate out of the box, nor have they stayed accurate with student use.

I have an old blue colored alcohol thermometer in a steel case which is still accurate to within one half degree. A dial thermometer that I bought fifteen years ago has similar accuracy. However a 20+ year old dial thermometer that I dropped a few feet is now reading 6 degrees high. I use it to measure water temperatures when mixing powered chemicals. I have some mercury thermometers at work, but usually use the alcohol based ones.

I have some mercury thermometers at work, but usually use the alcohol based ones.

 

We've had a really difficult time settling on a good, reliable mercury replacement.

 

The cheap red(or blue) alcohol ones are not terribly accurate or repeatable, and have a somewhat limited temperature range.

 

One of our last hold-outs were for tasks that need higher temperature thermometers(up to say 200º or 225º or so). We did find some serviceable ones. I'm not sure what they're filled with-it's a blue liquid that's just trademarked as something like "Enviro-safe" without actually telling us what it is, and they don't have much if any smell when they break. They fine except that the columns will break if you look at them cross-eyed. We've invested in storage trays that hold them bulb-down at about a 5º angle, but of course that is still at the mercy of the apparently overly complex task of actually placing them in the trays pointing the correct direction or actually returning them to the trays in the first place. I've even seen columns break in the course of something like a distillation where there was a bump that splashed up on the bulb and then rapidly evaporated off. Broken columns are nowhere as easy to repair as mercury-they don't shake down appreciably, and even freezing the bulb can be hit or miss(dry ice/acetone often won't pull them down enough, and liquid nitrogen usually freezes the liquid and causes the bulb to break off).

Thermoworks has some digitals that might be interesting, including a reference thermometer. The less expensive ones are .9F accuracy, but that's over the entire range. Likely much better where you're going to use it. (also great if you cook) Mercury thermometers are getting to be rare birds and really shouldn't be used in a darkroom anyway. Mercury is a strong sensitizer if you break one. I've used an Omega dial for decades and it's always within a half degree compared to my lab thermometers.

Rodeo Joe might be right. I have a couple of laser thermometers, mostly for cooking, and they disagree on temperature from one to the other by a couple of degrees. But then my two regular thermometers (both of identical type) also disagree. Not sure how you know which one is correct.

+1 to 'Get a digital one'.

'Cheap and accurate', not so much.

 

I've got several 'cheap' digital thermometers, including two supposedly designed for laboratory use. None of them came 'accurate' out of the box. Typically a degree or so out.

 

Not really a problem as long as you know that it reads 0.8 degrees low at 20 C, or whatever. But to find out you either need another known calibrated thermometer, or to spend some time with crushed ice and water, and boiling distilled water baths. Not forgetting to make allowance for the current atmospheric pressure in your boiling-point calibration.

 

It might be easier in the long run to get a 'Brannan', or similar laboratory certified glass thermometer, against which to calibrate your cheap digital thermometer. Keeping the glass thermometer safe in its keeper and using the robust digital one for everyday use.

 

Working in a lab I've seen the local certified thermometers being recalibrated. It was a job that took someone several weeks every year & some of the highly precise glass thermometers proved to be out by a significant margin after a few years.Our master thermometers used in the calibration had to be sent away every year for NAMAS recertification.

I'd be surprised if a alcohol in glass type sold for photography proved to be accurate at all even if it is reasonably precise (two very different things).

Cheap digital ones are unlikely be much worse & for photographic purposes consistency is more important than accuracy IMO.

You can still buy new mercury lab thermometers. For instance: Precision Mercury Laboratory Thermometers

On the slim chance that you live near me (Wisconsin), I have a Kodak I don't use any more.

Get a digital one at the grocery store. They're cheap and accurate.

I have many but none is accurate. To get the kind of 1/2 degree C accuracy I would have to pay big buck. Over $1000 I would think. Most of them do have decent repeatability so you would need an accurate thermometer and calibrate these at the temperature that you need for you process.

Edited September 7, 2020 by BeBu Lamar

To get the kind of 1/2 degree C accuracy I would have to pay big buck. Over $1000 I would think.

It's nowhere near that amount of money to get something accurate to 0.5 degrees.

 

For B&W developing, within 1 degree is accurate enough, and home colour developing is too expensive to buy just the chemicals these days.

 

The misleading thing about digital thermometers, is that they show 0.1 degree increments. Whereas they might well be a degree or two out. But so might a liquid-in-glass thermometer if you don't immerse it to the correct depth.

....for photographic purposes consistency is more important than accuracy IMO.

Absolutely!