Weston’s Amidol (for paper)

03 aprile 2006  Pier-Luigi  Formule (0)
Amidol is the dihydrochloride salt of 2:4-diaminophenol. It was introduced as a developing agent in 1892. No accelerator is necessary in amidol formulae, it being such a powerful agent that the sulfite preservative alone provides sufficient alkalinity for development to take place. In fact, amidol is one of the few organic developing agents that remain active in a slightly acidic solution. A mild acid (usually citric, but sometimes acetic, boric, lactic or tartaric) is often added to amidol formulae to prevent oxidation, which can cause staining of the print. The acid also acts as a restrainer. Potassium bromide is said to have little restraining effect upon amidol except in large quantities, but is always added to prevent fog and staining. With no bromide or acid added, or if the solution is too hot, amidol will stain prints a rosy pink color. Amidol is highly toxic and can cause severe allergic reactions similar to metol, bronchial asthma, gastritis, convulsions, and coma. Handle the dry powder with extreme caution and do not breathe the dust. Amidol’s oxidation byproducts stain fingers and fingernails and leave a black deposit on the bottom of the developing tray, which can cause stains on the print if it is turned upside-down. Amidol also stains tongs, which sometimes leave marks on prints--hence, a wide border around the print is desirable. Amidol gives off noxious fumes when mixed with hot water, so most formulae recommend mixing at room temperature, or allowing the solution to cool before adding the amidol. Fresh Amidol is a white to grey crystalline powder that dissolves readily at room temperature, but as it ages it turns dark and becomes more difficult to dissolve. If you find it necessary to mix amidol in hot water, do so under a fume hood or outdoors. There is evidence that under certain circumstances amidol begins development from the bottom of the emulsion--when in solution with bisulfite (for film) according to Jacobson and Jacobson, or when in a strong acid solution (for paper) according to Paul Schranz. Schranz states: “As the developer penetrates the emulsion layer, it becomes less acid due to its reaction with the gelatin. ...at some depth the pH rises high enough to permit development to start.” A great many of the standard formulae are quite similar. Bernard Jones’ Encyclopedia of Photography (1911) lists two formulae that are nearly identical with the Ansco formula given above. I am most familiar with the Ansco 113 formula, having used it many times. Even with 2 grams of citric acid added I usually find it necessary to dilute the solution somewhat, yet it still makes a very rich, contrasty print. I have used Weston’s formula on several occasions, but didn’t find that it provided any advantage over Ansco 113, though my notes indicate I was only adding 10 ml. of 1 benzotriazole, whereas it appears that Weston may have added as much as 60 ml. I have, however, used Samuel Fein’s formula extensively. Fein eliminates the bromide altogether, substitutes benzotriazole, increases the sulfite, and adds a whopping 13.5 grams of citric acid. His formula gives an exceptionally brilliant tonal rendition and a very cool image color. It provides the coldest tone and the greatest contrast I have been able to achieve with Azo. Interestingly, Michael Smith recommends reducing the amount of bromide for developing Azo, as does the Ilford ID-30 formula. Michael Smith wrote to me to note that he rarely develops Azo longer than one minute. He says the more you extend development, the colder the image becomes. In testing his formula, I found that to be true, and when I gave the prints very full exposure and developed for only one minute I found that I got the most remarkable high-value separation I have ever achieved with the 8x10 negatives I was printing, while still retaining the deep blacks amidol is famous for. The reduced development time produced prints with a slight greenish cast, which was easily removed by 1 minute in Kodak selenium toner (1+15). Prints thus toned show a remarkably neutral color. More than one minute in the toner causes the prints to turn an unpleasant purplish color. Increasing the development time causes the print color to become blue-black, which toning does not as easily alter. Balagny’s amidol is a very old formula of the type that is said to begin development from the bottom of the emulsion up. I tested this developer in 1991. Mixing the bisulfite solution was exciting--I put on my acid-proof gloves and safety goggles and went outside to do the mixing. I held the saturated bisulfite solution at arms length and slowly added the one dram of strong sulfuric acid. The mixture boiled and fizzed. Later, I foolishly added the amidol to the hot solution of other chemicals and had to leave the room in haste to escape the fumes. Please handle all these chemicals with extreme caution. The image produced by Balagny’s amidol was neutral to warm, becoming much warmer with increased dilution, and was relatively soft. Seagull and Zone VI Brilliant both produced slightly warm blacks and became purple-brown when toned in selenium. Brovira produced cold blue-blacks, which only seemed to get colder with selenium. The image did not begin to appear until a full 50 seconds into the development, and development times ranged from 2.5 to 4 minutes. In future, I would like to try this developer with Azo to see if it warms the image any. The Peckham formula is interesting in that it uses equal amounts of catechol and amidol, and substitutes sodium chloride for potassium bromide. I find it to be very clean working and economical, especially when diluted 1:1 with water. I have used it extensively for developing Azo. The Lootens formula keeps sulfite content low, uses very little bromide, and adds small amounts of citric acid and potassium thiocyanate. I found it to be somewhat softer working than either Agfa 113 or Fein’s Amidol. The image forms slowly--my developing times ranged from 2 to 4 minutes. This formula produces a very neutral print color, and because of its low alkalinity it keeps well in the tray. I used it with a citric acid stop, as Lootens recommended. I haven’t tried Below’s formula yet.


Water, 70º F 800 ml Sodium sulfite, desiccated 35 g Amidol 11 g Potassium bromide, 10 sol. 7.5 ml BB Compound 60 ml Water to make 1200 ml



BB Compound consisted of benzotriazole--probably in a 1 solution. Weston also added 5-10 grams of citric acid as a preservative.

Aggiungi Commento