Any good use for a ph meter in the dakroom? They are readily and affordably available on the big auction site, even surplus lab grade stuff. I could see it being useful for testing things like developer and stop bath, even wash water.
Anyone use one?
Every time I scratch mix chemistry! A decent meter is an essential for formulating color chemistry. The pH meter is as important as an accurate thermometer and a timer. One must be careful to calibrate the meter at each use with known-good standard solution, usually pH 10.00 in my case. You also want to use a meter that is temperature compensated.
Many of the lab surplus meters available on the web are not practical because they require expensive electrodes that are difficult to find and have short lives. An accuracy of +/- 0.1 pH unit is plenty good for most photography, so it's not necessary to keep a large lab-grade meter around. I am currently using a Hanna pencil-type meter that reads digital values and works fine for my purposes.
By denying the facts, any paradox can be sustained--Galileo
Thanks for the reply. I see a lot of mention of pH levels here on APUG for various chemicals, especially in discussions of one brand over another etc, but never a thread on pH meters or measurement. Seemed kind of odd to me. I guess strips would work well too but fishing them out of a can is kind of fiddly, especially if you are mixing chemicals and may have wet hands.
I don't scratch mix anything in my darkroom but I figured knowing pH might be a good standard to judge chemistry life or troubleshoot problems. Guess I was right I'll have to add one to my short list
pH paper strips are good in a pinch, or for qualitative work, but in the darkroom I think they'd be more misleading than anything. A good pH meter that can be calibrated to two points is best. mts is right about the electrodes. Temperature compensation is helpful but not necessary as long as you calibrate and measure at the same temperature.
In standard b&w silver processes with off-the-shelf chemistry there is nothing to test or adjust, with respect to pH.
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There are paper indicators on the market offering a resolution of 0.1 (depending on range).
Concerning this resolutions I rather spend money on several rolls of these as on a delicate electronic ph-meter.
The situation would be different, in case the needed resolution and accuracy would be higher, or ph-metering would often be done, and thus taking a lot of paper.
Another aspect are colourings of the tested fliuds. Such can make use of paper strips difficult.
Last edited by AgX; 10-15-2009 at 07:48 AM. Click to view previous post history.
Other than your water supply. It should be fairly constant, but things happen.
Originally Posted by ic-racer
I read an old book of film processing that the most influence on the developing process is alkaline substance of developer. Any elementary logic shows that the developing substance is very important. So, in a developer solution pH is very important. If you allow material possibilities - is very good to have a pH meter. If you have money only for pH indicator paper - it is good. If you have not a good pH meter electrodes - better not use it. If you have no pH indicator paper you have to know everything about photographic chemistry.
I personally, rarely use indicator paper to check myself to various tests.
In general, no sudden changes occur in the processing solutions than by serious errors.
In this case, I change the solutions.
Yes, go for it. For the price of a couple of rolls of film you can get a cheapie off the 'bay and they seem accurate enough for our purposes. Cheap as chips. They help in understanding the finer points of developer activity over time and and varying conditions. You won't regret it. Paper strips - nah! Too fiddly by far.
Settle on a standard - eg borax at the alkali end and sodium tartarate at the acid end (cream of tartar).
I have several times found solutions to my problems with it when logic dictated that all should be well - but it wasn't - the stuff had gone off.
Want to know the difference between Kodalk and borax or carbonate? do a simple test. My Diafine 'A' bath was off but looked fine until I checked the pH. A failed film put me on to that. At least I came away knowing it wasn't me! Just keep it clean, and dry carefully between uses. Calibrate regular.
I found mine, an omega electrinic unit at a hydroponic 'grow op' supply shop. It cost a bit more that $100 a few years ago, plus $18 for three good sized bottles of 4, 7 and 10 buffered calibration solutions. Stick the probe in the test solution, press cal, let it blink 30 times, press confir, and you are calibrated for the session. Calibrate near the pH of what you will be measuring.
If I was buying all over again, I would spurge for a temperature compensated one. It is nice to be able to measure pH of developers as you mix them, because any adjustment of alkali, or countering with an acid can be easier to dissolve while the solution s still warm. Doing the math while mixing to figgure out ph shift due to termerature of the measured solution is a pain.
my real name, imagine that.