You know, the late Barry Thornton put forth the "two teaspoons of sodium sulfite" theory of film developing. The very much alive Ken Lee put forth the "two teaspoons of sodium sulfite" hypo clearing theory.
I can measure two teaspoons consistently. I could also weigh two teaspoons of sodium sulfite on my OHAUS balance scale or my digital scale. Anyway you cut it, it's still two teaspoons.
Now, tell me, what would you say in my place?
one must (should) do everything possible to eliminate as many of the variables possible
and... sheesh! guys, the OP asked a simple question....and all but one jumped on him for measuring his chems with a teaspoon. Nice. What a nice bunch of helpful folks....
Oh rats, I just composed a long and obviously brilliant comment for this thread. Then I pushed the wrong button and lost it!
Though you weren't asking me, I think I've got an answer: I'd say pretty much what you're saying. The thing is, I'd have the same answer for Patrick Gainer if he asked that question.
As someone who lurks most of the time, and for whom much of the pleasure of analog is in messing around with darkroom processes, as an engineer by profession and a scientist by training, I really appreciate these discussions of process that you guys seem to have periodically. I've learned a lot from reading both of your posts, and tend to think that you're representing complementary approaches, both legitimate.
I have the impression you feel a bit ignored by the readership---a voice in the wilderness for a thorough understanding of process and tight quantitative methodology, while readers breeze past your stuff because it's difficult and run around looking for the easy answer. I can only speak for myself, but I think there are a lot of people in my position, reading your posts, thinking about them, taking things you've said into account while going about the business of turning photons into silver, but not necessarily posting about it.
Well, this is my post about it: I'm listening. Thanks.
But I still make Caffenol with volumetric measurements.
-NT
Now, tell me, what would you say in my place?
PE
Oh rats, I just composed a long and obviously brilliant comment for this thread. Then I pushed the wrong button and lost it!
Absolutely. And there isn't an engineer who will tell you otherwise.
If the wood block needed to be more precise then the dimensions would be specified 12.0 x 12.0 x 12.0 and any dimension from 11.9 to 12.1 would be acceptable.
If you look at an engineering drawing you will find they all specify tolerances. Usually the tolerance is implied by the number of decimal places used in the dimension. If it is a critical dimension it may be specified as, say 12.354 -0.000/+0.001 inches. Any dimension without a tolerance is suspect.
I think this is something for testing.
With volume measuring you will have a variable desity of cristals in a given volume.
So measure the weight of 10 volume samples and look how much it varies.
That variation should be taken into account to the above: is a 20% or 10% variation of each of the chemicals mentioned above noticable in the end result ?
By reasoning I think you will get more consistant results by measuring by weight than by volume, even if there are more variables into the play like the consistancy of your film/paper.
Peter
Aren't teaspoon measurements perfectly appropriate for some applications, where exact measurements aren't critical? What if all I want to make is a citric acid stop bath?
KBr ... weigh it once to make a standard solution
Aren't teaspoon measurements perfectly appropriate for some applications, where exact measurements aren't critical? What if all I want to make is a citric acid stop bath?
fotch;842641...an argument in favor of sloppiness.[/QUOTE said:I think you may be the only one making that argument.
Knowing how much is very important. That's why there is a tolerance on all quantities. The tolerance does not say "cut a bit of wood to 12.00 inches as best as you are able" - because, quite frankly, the person making the cut may not be able enough. Instead it says that in this application - a tooling fixture made of rock maple as an example - the length is only acceptable if the cut is between 11.99 and 12.01 inches. But if it is a bit of wood destined for propping the outhouse door then 12 inches plus-minus an inch is sufficient and someone making a cut to 1/100th of an inch would be considered touched by the sun.
The argument for specified tolerances is an argument for precision and is well beyond some exhortation to measure as best as you can. 'As best as you can' is just too damned sloppy a great deal of the time.
There are those of use who are convinced that B&W photographic chemistry tends to the outhouse-door-prop end of the tolerance spectrum.
Those who are convinced otherwise are under no compulsion to do other than measure out chemistry in any way they please. Ditto the teaspoon crowd.
A quick experiment - scooping 14 1tsp samples of of metol - shows a CV of 5% in the weight of the sample.
The effect of concentration on kinetics depends on many variables. See Mees revised edition, 1972, chapter 15. A general windage/rule of thumb is that development time for constant gamma varies 25% of the variation in developing agent concentration. Following this, a 5% error in developing agent would require a 1.2% change in developing time - for a typical 7 minute development that is equivalent to a time change of 5 seconds or a temperature shift of 0.25F.
Well, Sandy, you make stock solutions of your Pyrocat series and from there on it is volumetric measurements to make the working solution. You see the virtues of both. There are some chemicals that are best made into stock solutions. When you are working with developer stocks that are "put up" in glycerin or glycol or TEA, and have other stock solutions that contain the necessary alkali, you are well fixed to mix any combination of those to suit your fancy, if not your foreknowledge of the results. If you say to use 1 part A, 2 parts B and 100 parts water we know you have tested that combination. That doesn't keep us from wondering what would happen if we changed the numbers, and trying it out just for fun.I really don't get it. The price of a good quality electronic balance is not that much more than the cost of spoons?
Why would anyone choose to handicap their work with imprecise measurements?
I hate to disagree with people whose opinion I respect, but my experience is that in many cases a difference of 0.2g in a developer formula of total of 1000 ml makes a big difference in results.
If you are on a desert island and have to do with lack of precision, ok, but with UPS, FED-EX, DHL and the USPS why do so if you live in the lower 48?
Sandy k ing
Well, here is one of the problems. HQ is normally sold either as fine brown needles or as a fine brown powder. In one case, the HQ is in its native state as it crystallizes, (needles) but some companies grind it to a powder so they can ship it more compactly. The powder, weight for weight takes up less volume.
The same is true for KBR which is sold as cubic crystals or fine powder. Same reasoning as above. The powder is effectively more dense.
I have tested the KBr, as I have stated earlier, and found that 1 unit volume (any volume) can vary by over 20%. So, if you can stand that in your work, then by all means go for it. But, from a repeatability standpoint you could be adding anywhere from 0.8 to 1.2 g/l of KBr. This might work in Dektol, but would kill you in color work and would change many other formulas as well, in ways I cannot predict.
An added factor is the problem of leveling off a teaspoon full of fine powder vs needles or cubes. The cubes or needles are very difficult to level and this can vary in itself.
PE
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