I think the rule of thumb is 20 drops ~ 1ml, but a drop is not a standard unit of measure. I measured a few of my droppers and they varied between 18-23 drops/ml.
I have a small plastic bottle (about 60 ml) designed for dispensing liquids drop-by-drop. I use it for Kodak Photoflo 200. Based on quick tests, I find 60 drops equals 5 ml (12 drops equal 1 ml).
Mike do you remember what % the Gold solution was that we used, 1%, 5%, 10%? Mike, it could work out to be more or less $10.00 per 8x10, probably more with the addition of the paper and Gold. 4x5s or 5x7s are looking good. I happen to like the size of the 5x7 I made, it's large enough to be seen and yet has the Jewell like quality. I see CT prints in a larger size like Jim does.
I looked up the drop question to see if there was any specific scientific number and what I found was 20 as Barry said. It depends on viscosity, temperature, time of day, date of full moon and others but 20 is the number. Now to find the dropper that was used to determine that number.
You must calibrate the dropper for each solution you use. Droppers vary in tip size over a wide range, and the viscosity and density of the solution change the drop size. A heavier solution will drop off a given tip more readily than a light one for example, or a thick solution will drop off more slowly.
Curt
Make sure you are using the plastic (molded and accurate).
Don't use glass- too variable.
And when you get to do larger prints (>5x7) consider using the right pipettes with pipette pumps. Much faster and more accurate than drop counts. Heck, I'd be at it all day if I were to count out drops for 12x20 and 7x17. Even 8x10 and 11x14 is faster with pipettes.
Well if I can think back to pharmacy school which is about 10 years ago now. 1 minum is equal to .0592ml of water. But indeed, viscosity and density would certainly change the size of the drop.
In addition to the liquid that is measured, the drop count 'could' change based on if the dropper is held vertical or at an angle...depends on the total volume. Best way to find out is to measure and then always try for the same conditions each time. Or depending on what you are doing, it may make no difference at all. I do not worry about it when I measure for pt/pd prints, but do try to always do it the same way.
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