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Photo Forum / Film Photography / Darkroom / May 2005My thermometer is woefully inaccurate; read about the shocking truth!
Hi all, I was mixing up a batch of KHCA this evening when I was surprised to find that my thermometer was reading 80 deg. F. for the water running from my tap. Not only did it feel cooler than that, but it just seems kind of odd, this time of year, where I live in the Northeast, for tap water to be that warm. I went along with this for mixing my KHCA but then the contradiction between the sensation of "cool" and the high temperature reading got to be too much. So I borrowed a kitchen thermometer from next-door and, sure enough, my termometer is reading 30 degrees hotter than the other thermometer (yes, they are both in Farenheit)! The implications of this discrepancy are chilling (no pun intended). I've been using this termometer for well over a year now to develop my film. I've been operating under the assumption that my developer is at 75 deg. F., and yet the developing times I've needed to achieve a zone VIII density of around 1.15 have run consistently higher than predicted by the big developing chart. For example, at 75 deg. the big chart calls for developing TMY in xtol 1:1 for seven minutes. I've been needing to develop for up to 11 minutes! TMX is supposed to take 5 minutes; for me it takes 7. My theory is that, all along, this thermometer has been reading _relatively_ warmer than the true temperature. So all this time I've maybe been developing at 65 deg. or so and,hence, have required a longer time. So, up to now, the thermometer has been neurotic, off by about 5-7 degrees. But tonight it went off by 30 degrees, in other words, it went psychotic. Other than hearing expressions of empathy and shared experiences (like, maybe it's not just _me_), I'm hoping that folks can answer a few burning (pun intended) questions. First, I have a room thermometer that I use to keep an eye on the ambient room temperature to anticipate temperature drift of the fluids. I've noticed that my fluids left to sit in the room, by this darkroom thermometer, consistently read about 5-7 degrees warmer than room termperature. That is to say: if my room thermometer reads 68 deg., and I leave the the fluids in the room for the better part of day, by this thermometer the fluids are at 75 deg. Not being a chemistry geek, I've been assuming that this discrepency must just be the way it is. But now I'm realizing that this discrpency may completely confirm my diagnosis about my developing times. Am I right about this? Secondly, the KHCA package tells you to mix the KHCA at 80 deg. F. So this evening I must have been mixing it at, at best, 60 deg. F. Does this matter? Almost all of it disoved -- there was just a bit of granules in the bottom of the vessel that were still swirling around. Am I ok as long as most of it dissolved, or is there something magical that's supposed to happen at 80 deg.? Thirdly, is it possible that I hosed up this thermometer by allowing it to be exposed to hot tap water? I wash my vessels in hot tap water and when I wash them I was the thermometer, too. Is it possible that doing so is what screwed it up? Or is a $17 thermometer (analog dial style) from B&H just not trustworthy enough? Finally, please recommend a good, reliable thermometer. I don't want this to _ever_ happen _ever_ again. There are just too many variables in this biz. to have to worry about this sort of thing. Thanks for your help. --Phil [edited] > First, I have a room thermometer that I use to keep an eye on the > ambient room temperature to anticipate temperature drift of the fluids. [quoted text clipped - 6 lines] > I'm realizing that this discrpency may completely confirm my diagnosis > about my developing times. Am I right about this? Maybe. Discrepancies of +/-30% in developing times aren't that unusual depending upon exposure, agitation, enlarger light source and paper. > Secondly, the KHCA package tells you to mix the KHCA at 80 deg. F. So > this evening I must have been mixing it at, at best, 60 deg. F. Does > this matter? Almost all of it disoved -- there was just a bit of > granules in the bottom of the vessel that were still swirling around. > Am I ok as long as most of it dissolved, or is there something magical > that's supposed to happen at 80 deg.? It should dissolve faster at 80F, however, all of the powder should go into solution if allowed to stand overnight. If a precipitate remains, filter the solution before use. > Thirdly, is it possible that I hosed up this thermometer by allowing it > to be exposed to hot tap water? I wash my vessels in hot tap water and > when I wash them I was the thermometer, too. Is it possible that doing > so is what screwed it up? Or is a $17 thermometer (analog dial style) > from B&H just not trustworthy enough? Some dial type thermometers may be "adjusted" by turning the stem relative to the dial. If yours is "adjustable", you might calibrate it and lock it with epoxy. I'd suggest that you drop a note to Henry Posner explaining the problem, return the thermometer, and swap it for one of the liquid thermometers such as the Kodak Darkroom Thermometer F Scale (Black & White - $9.95), or a similar color thermometer (I use a Jobo). > Finally, please recommend a good, reliable thermometer. I don't want > this to _ever_ happen _ever_ again. There are just too many variables > in this biz. to have to worry about this sort of thing. Good luck. Don't worry about the actual numbers - let the prints be your guide. Mike Fluids left at room temperature should eventually be also the same temperature as your room -- hence the name. Your HCA is probably fine, just make sure all the crystals are gone, reheat if necessary. I have one of my thermometers in a gizmo called a well which screws onto the end of the tap once I twisted it by accident and I noticed that the scale rotate too. I used a second to establish the correct temperature again. I also once went to Walmart and bought a $8 indoor/outdoor thermometer which has a six foot sensor (outdoor) it is remarkably accurate to about +/- .1 degree. It's great for quick reading bath temps, dev temps or when I'm just cooking a batch of Potassium Dichromate [insert evil laugh here]. In short I depend on it. I think you've made the lesser mistake of underdevelopment. So you negs are a bit flat, just crank up the contrast a grade or two and everything's more or less fine. > Hi all, > [quoted text clipped - 59 lines] > > --Phil > First, I have a room thermometer that I use to keep an eye on the > ambient room temperature to anticipate temperature drift of the fluids. [quoted text clipped - 6 lines] > I'm realizing that this discrpency may completely confirm my diagnosis > about my developing times. Am I right about this? Some chemical reactions will generate heat. Some will actually cool down. But over time anything left at room temperture should end up at room temperture. I always do my B&W at room temperture which in the basement is fairly well controlled year round. > Thirdly, is it possible that I hosed up this thermometer by allowing it > to be exposed to hot tap water? I wash my vessels in hot tap water and > when I wash them I was the thermometer, too. Is it possible that doing > so is what screwed it up? Or is a $17 thermometer (analog dial style) > from B&H just not trustworthy enough? Is it adjustable? It may have a nut or something on the back. > Finally, please recommend a good, reliable thermometer. I don't want > this to _ever_ happen _ever_ again. There are just too many variables > in this biz. to have to worry about this sort of thing. Whatever one you get should be checked. Then checked every so often afterwards. Ice water test for the low end. I use a digital fever thermometer to check the area around 100F. The fever thermometers are cheap but fairly accurate. Nick Thanks to all for the rapid response. As suggested, I am indeed able to adjust the thermometer by rotating the dial relative to the stem and, also as suggested, I calibrated in hot water using a digital fever thermmeter. What puzzles me is how it could have gotten 20-30 degrees out of adjustment without having been rotated deliberately: I had to hold the stem with a vice-grip in order to do the adjustment. My negatives up to now have been fine because I've been looking at the them with a densitometer, so I ended up with the right development time for the temperature that, for most of the time, was inaccurate in a consistent way, until this recent change that took it so far out of range. --Phil > my termometer is reading 30 degrees hotter than the other thermometer > ... it was a B&H $17 dial t. ... can you suggest a new one? That is all that needs be said. Cheap dial thermometers aren't reliable, but you know that ... Glass thermometers will just about always read correctly but they are slow and they break. It is a good idea to have a "Kodak Color Thermometer" around as a calibration check - look on ebay. I find the digital pocket/stem thermometers sold for cooking work well. Look on Amazon. Taylor makes a waterproof (cough) one for about $15. Digital health thermometers may not be accurate, or read out, over a wide temperature range. > I don't want this to _ever_ happen _ever_ again. Ha!  SignatureNicholas O. Lindan, Cleveland, Ohio Consulting Engineer: Electronics; Informatics; Photonics. To reply, remove spaces: n o lindan at ix . netcom . com psst.. want to buy an f-stop timer? nolindan.com/da/fstop/ > Hi all, > [quoted text clipped - 103 lines] > > --Phil You haven't said what type of thermometer this is. If its one of those large dial thermometers its adjustable. An old friend of mine who is a design engineer says that anything adjustable is, by definition, out of adjustment. Adjustable dial thermometers need to be checked against an accurate thermometer frequently. I have two standard thermometers I compare others to. One is a calibrated process Mercury thermometer with a 12" column. The other is an electronic thermometer called a Check-Temp made by Hanna Instruments Co. Its not expensive and is more accurate than the Mercury thermometer. I have a dial thermometer, which is the one I actually stick into solutions, but I check it frequently against one of the others. http://www.hannainst.com/index.cfm The one I have is at: http://www.hannainst.com/products/testers/testers.cfm?ProdCode=Checktemp%20-%20C hecktempL Generally, using a thermometer at any temperature it will display will do it no harm. Dial types usually use bi-metallic strips and are very rugged. I think you have an adjustable type and just twisted it at some point. The temperature recommended for KHCA is low because Sulfite does not need high temperatures to dissolve. 80F is a reasonable temperature. If the temperature is too high it can cause some decomposition of the sulfite but, AFAIK, that is much higher than 80F. At low temperatures the stuff may just take a long time to dissolve. A 2 degree error in developer temperature is significant for B&W. Signature--- Richard Knoppow Los Angeles, CA, USA dickburk@ix.netcom.com Hi Richard, Yeah, this one is definitely adjustable. What puzzles me is how it could have gone out of calibration when it is so hard to move it: I had to grab the stem with a vice-grip to adjust it. Having finally rid my home of mercury thermometers, I am loathe to get another one for this purpose. I'll look into the digital model you suggest. Many thanks! --Phil > Hi Richard, > [quoted text clipped - 13 lines] > > --Phil My Weston is also pretty stiff but it has gotten out of adjustment anyway. This is my working thermometer. I use the CheckTemp to standardise it. I have four mercury thermometers none of which exactly agree with the others. One of them agrees exactly with the CheckTemp so I use that as a backup standard. Absolute calibration of thermometers turns out not to be trivial. There are a rather large number of variables that one needs to know about and control. Relative calibration, that is matching two thermometers, is relativly easy. A thermometer with a stable and constant error can be worked with since its error can always be compensated. Its having something that can read anything at all that can drive you up the wall. Signature--- Richard Knoppow Los Angeles, CA, USA dickburk@ix.netcom.com > My Weston is also pretty stiff but it has gotten out of > adjustment anyway. This is my working thermometer. I use the [quoted text clipped - 9 lines] > compensated. Its having something that can read anything at > all that can drive you up the wall. I have a little Weston Mirroband with about a 1.5" diameter dial. I also have one of the very expensive Kodak Process Thermometers Type 3 (mercury) that can be read to about 1/4 degree C. It comes cemented into a stainless steel sheath so it is more difficult to break than a glass-only mercury thermometer. The box says $52.25, which is no doubt what I paid for it when I bought it decades ago. I imagine they would be over $100 if you could get them anymore. The data sheet says it is accurate +|- 0.125C at 15C, 20C, 25C, 30C, 40C, and 50C and +|- 0.25C over the rest of the scale. The datasheet was copyright in 1980, so that gives an upper bound on when I bought it. I doubt E.K. sent each one to the National Bureau of Standards to calibrate them, but they may have calibrated them against their own thermometers that may have been calibrated by the NBS. I assume my Kodak thermometer is the standard, and calibrate other thermometers vs. it. I run water from my temperature regulator valve into a beaker, and stick the thermometers in there after the temperature stabilizes. It turns out that at 75F, all my thermometers agree within +|- about 1/2 degree, with the one in the temperature regulator valve the worst of the bunch. It has hysteresis (I cannot be sure if it is the thermometer itself, or the regulator in the valve, though). Signature.~. Jean-David Beyer Registered Linux User 85642. /V\ PGP-Key: 9A2FC99A Registered Machine 241939. /( )\ Shrewsbury, New Jersey http://counter.li.org ^^-^^ 08:25:00 up 15:00, 3 users, load average: 2.23, 2.18, 2.12 >> My Weston is also pretty stiff but it has gotten out >> of [quoted text clipped - 57 lines] > the thermometer > itself, or the regulator in the valve, though). I don't think Kodak Process Thermometers are certified by NIST either but they are undoubtedly calibrated against a NIST certified standard. One must be careful when checking or using immersion thermometers to immerse them to the correct point. This is normally marked on the thermometer tube. I am sure you know that tube type thermometers come as either partial immersion or total immersion types (something like baptism). Thermometers for measuring air temperature are total immersion types. For very accurate calibration of partial immersion thermometers the temperature of the medium the the upper part of the thermometer is in is important. The old NBS handbook (the three volume one) has a section in it on thermometer calibration but is been so long since I read it I no longer remember what their exact procedure is. Off the shelf high quality Mercury thermometers are generally reliable to about +/- 2F which is not good enough for photography. A glass Mercury thermometer has the advantage that it does not age much. Once standardized its reliable for many years. Signature--- Richard Knoppow Los Angeles, CA, USA dickburk@ix.netcom.com Richard Knoppow wrote (in part): >> The data sheet says it is accurate +|- 0.125C at 15C, 20C, 25C, 30C, >> 40C, and 50C and +|- 0.25C over the rest of the scale. The datasheet [quoted text clipped - 6 lines] > > I don't think Kodak Process Thermometers are certified by NIST either It seems to me that if they were, Kodak would have said so, since it would be a selling point (and a justification for a higher price). > but they are undoubtedly calibrated against a NIST certified standard. > One must be careful when checking or using immersion thermometers to > immerse them to the correct point. This is normally marked on the > thermometer tube. It is on the Kodak Process Thermometer Type 3; there is a line etched on the glass tube. But it does not way what the (presumably) air temperature above the line should be. If I were in Verkhoyansk, Siberia in the winter (120F below zero sometimes), or in a shack with a black roof in Death Valley, it might make a difference. But I do not know if it would be photographically significant. > I am sure you know that tube type thermometers come as either partial > immersion or total immersion types (something like baptism). I suppose mine is a Presbyterian thermometer, not a Baptist one. ;-) > Off the shelf high quality Mercury thermometers are generally reliable to > about +/- 2F which is not good enough for photography. A glass Mercury > thermometer has the advantage that it does not age much. Once > standardized its reliable for many years. @ $52.25 around 1980, I suppose mine is not off-the-self. I bought it from the last good local photographic store (that has since gone out of business). Also, the two local custom photo labs are now gone, so only O'Photo and MotoPhoto (1-hour shops that process only 35mm) remain. I tried one of them, and they got too much dirt in the emulsion of the test roll I gave them, so I never went back. Signature.~. Jean-David Beyer Registered Linux User 85642. /V\ PGP-Key: 9A2FC99A Registered Machine 241939. /( )\ Shrewsbury, New Jersey http://counter.li.org ^^-^^ 12:10:00 up 1 day, 18:45, 3 users, load average: 2.49, 2.35, 2.32 >@ $52.25 around 1980, I suppose mine is not off-the-self. I bought it from >the last good local photographic store (that has since gone out of >business). Also, the two local custom photo labs are now gone, so only >O'Photo and MotoPhoto (1-hour shops that process only 35mm) remain. I tried >one of them, and they got too much dirt in the emulsion of the test roll I >gave them, so I never went back. Elco Color Lab went out of business ? JD - www.puresilver.org >>@ $52.25 around 1980, I suppose mine is not off-the-self. I bought it from >>the last good local photographic store (that has since gone out of [quoted text clipped - 6 lines] > > JD - www.puresilver.org I was referring to Fishkin Brothers in Perth Amboy, NJ. for the "local" photographic store. Locally, the best lab was PhotoWorks in Red Bank, but Jess Cohen retired and sold the business to a couple that should have been selling Tupperware for all they knew about photo processing. Now Dorn's in Red Bank is going out of business too. None can compete with the digital cameras for all the throw-away shots most people make. Signature.~. Jean-David Beyer Registered Linux User 85642. /V\ PGP-Key: 9A2FC99A Registered Machine 241939. /( )\ Shrewsbury, New Jersey http://counter.li.org ^^-^^ 18:30:01 up 2 days, 1:05, 3 users, load average: 2.49, 2.41, 2.35 >> Elco Color Lab went out of business ? >> [quoted text clipped - 9 lines] >Now Dorn's in Red Bank is going out of business too. None can compete with >the digital cameras for all the throw-away shots most people make. Do consider El-Co sometime. http://www.elcocolor.com/ JD - www.puresilver.org > Hi Richard, > [quoted text clipped - 13 lines] > > --Phil I meant to add to my post that I don't use the CheckTemp directly because it won't take immersion. Use it to standardise your dial thermometer and use that. The dial unit won't be hurt if you drop it into a tank of something. Signature--- Richard Knoppow Los Angeles, CA, USA dickburk@ix.netcom.com |
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