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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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 Originally Posted by archphoto  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 If you can find it, read my article in Petersen's Photographic, April 1973 issue. I did exactly that. I discribed what I did in my recent post here in reply tp PE.
Borax is a point in question where measurement by weight is not reliable. There are two states of hydration: Pentahydrate and decahydrate. Both can and often do exist in the same batch. The best way to measure borax, even if it is reagent grade, is by volume of a saturated solution. A saturated solution at, say, 15 C will be equivalent to 3.79% by weight of the decahydrate, whether pentahydrate or decahydrate or a mixture went into the solution. The clear liquid of that solution, stored at a higher temperature, will remain at 3.79 weight percent and very nearly that same percentage by volume. If you feel compelled to weigh KBr eah time you use it, why not weigh it once to make a standard solution? Then the volume of a portion of that solution is as accurate a measure of KBr as you will be likely to need in ordinary photography.
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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?
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Originally Posted by Chazzy 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? That is reasonable.
PE
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There are some good points mentioned in this thread as for practical ways of making processing solutions. For example, if making a fine-grain B&W developer where 100 grams per litre of sodium sulphite is typical for many formulas, then being a gram or two out would probably go unnoticed. However, with some components such as Phenidone or one of it`s derivatives, then being as little as 0.1 gram out would very likely make quite a significant difference to the activity of the developer. I think that being as accurate as practicable is a good thing to do.
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Originally Posted by gainer KBr ... weigh it once to make a standard solution I believe that is the standard practice: a standard solution. Also of Carbonate (for adding to print developer), Ferricyanide and Phenidone.
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Originally Posted by Chazzy 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? I don't even think it's appropriate for the kitchen anymore. I'm not a great cook by any means, but I've always had problems getting consistency from baked goods like cookies. Some batches are good, some are too sweet, some are too flat, etc...
Then I bought a kitchen scale. Suddenly I'm consistent. Turns out simple measurements like "a cup of flour" can be all over the map depending on who is dipping out the flour -- because flour can compress. As can brown sugar -- how packed is "packed?"
This is why kitchen scales are common in European kitchens. I'm still wondering why it took *me* so long to figure it out and do something about it. Sigh...
All that said, I still use teaspoons -- for liquids, where they work correctly.
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[QUOTE=fotch;842641...an argument in favor of sloppiness.[/QUOTE]
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.
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Originally Posted by sanking 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, 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.
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Originally Posted by Photo Engineer 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 HQ is not a particularly good example for what I do with it. I have found that a wide variation in amount of HQ is tolerable in MQ or PQ developers where M or P are constant. The capacity of the developer is more determined by the Q, especially if the pH is buffered well.
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