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Photo Forum / Film Photography / Darkroom / January 2007EDTA, Calgon and developer formulae
I am having trouble with a fine white precipitate, I am assuming its Calcium, coming out of mix-from-scratch D-72 [Dektol w/o magic ingredients] stock solution. It seems the fix is to add calgon [sodium hexametaphosphate(?)] or EDTA. Question is: How much? Searching the web brings up 1tb/l of calgon, 10g/l of calgon, 1gm/l EDTA. Anybody use the stuff or know the recommended amount to add. Water here is reasonably soft, treated Lake Erie water.  SignatureNicholas O. Lindan, Cleveland, Ohio Darkroom Automation: F-Stop Timers, Enlarging Meters http://www.nolindan.com/da/index.htm n o lindan at ix dot netcom dot com Some of the Kodak formulas recommend 1 gram of CALGON (Sodiu Hexametaphosphate) per litre of stock solution. In the `Ilford Manual Of Photography`, 3 grams per litre is considere the optimum. It is recommended by Ilford that the CALGON is dissolve before the main components. Just a suggestion, but start with 2 grams per litre of stock solution -- Keith Tapscott. > Some of the Kodak formulas recommend 1 gram of CALGON > (Sodium [quoted text clipped - 6 lines] > Just a suggestion, but start with 2 grams per litre of > stock solution. You may also find it useful to boil the water. Boiling removes some hardness which is precipitated on the container (this is why tea kettles get crusty). The boiling will also remove dissolved gasses and coagulate any organic matter. Boil for about 5 minutes and allow to cool without disturbing. Then syphon off the clear water. Signature--- Richard Knoppow Los Angeles, CA, USA dickburk@ix.netcom.com -- Posted via a free Usenet account from http://www.teranews.com >> Some of the Kodak formulas recommend 1 gram of CALGON >> (Sodium [quoted text clipped - 13 lines] >Boil for about 5 minutes and allow to cool without >disturbing. Then syphon off the clear water. January 11, 2007, from Lloyd Erlick, I've used both sodium hexametaphosphate and EDTA for years. Both forms of EDTA take a little longer than sodium hexametaphosphate to dissolve, and they cost more. (The commercial product Calgon or Calgonite is now potsssium citrate, since phosphates are bad bad bad.) Toronto tap water is slightly hard, but far from anything people would taste as water hardness. I have found -- for my usual three liter mix of washaid -- that one quarter teaspoon of sodium hexametaphosphate suffices. It must be dissolved first in order to sequester the undesired metals (calcium and magnesium) first, then the components that possibly react with the metals (e.g. sodium sulfite, sodium carbonate) can be added. Boiling the water first is not necessary in Toronto. Kettles do get a coating inside over time, of course, but it takes a while. The water is treated municipally, and there is relatively little in it to coagulate. One of the good things about living in a city on a large lake ... Sadly, the things to worry about in tap water here are more of an industrial nature, like dioxins, which have been reported in a large blob of sludge that supposedly exists at the bottom of Lake Ontario. regards, --le ________________________________ Lloyd Erlick Portraits, Toronto. website: www.heylloyd.com telephone: 416-686-0326 email: portrait@heylloyd.com ________________________________ -- Richard Knoppow Wrote: > You may also find it useful to boil the water. Boiling > removes some hardness which is precipitated on the container > (this is why tea kettles get crusty). The boiling will also > remove dissolved gasses and coagulate any organic matter. > Boil for about 5 minutes and allow to cool without > disturbing. Then syphon off the clear water. and still add a sequestering agent -- Keith Tapscott. > fine white precipitate ... D-72 ... It seems the fix is to add calgon > [sodium hexametaphosphate(?)] or EDTA. Question is: How much? Results of a shot-in-the-dark trial: I have had no white precipitate from the addition of 1gm (1/4 tsp) of EDTA / litre of D-72 stock. SignatureNicholas O. Lindan, Cleveland, Ohio Darkroom Automation: F-Stop Timers, Enlarging Meters http://www.nolindan.com/da/index.htm n o lindan at ix dot netcom dot com > I am having trouble with a fine white precipitate, > I am assuming its Calcium, coming out of mix-from-scratch [quoted text clipped - 11 lines] > add. Water here is reasonably soft, treated Lake Erie > water. All that has been said about using EDTA and sodium hexametaphosphate is true enough, but there is another source of crud, especially with hard water. Be sure you completely dissolve each of the ingredients before you add the next and before you use the result. This is harder than many people realize, especially with hard water. Most of the ingredient will go into solution quickly, but some, often small, crystals are likely to remain even after a couple of minutes of stirring. These can cause trouble. You have to keep stirring until the solution is clear and no material is left either at the bottom or suspended in the solution. Using hot water helps. |
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