Fred Endsley

"Probably the most significant problem in the use of the blueprint, though, is a psychological rather than a chemical one. We find that we are working against a cultural or conventional color bias: the blueprint is simply too blue. Reasonably neutral black seems to be an ideal, but another 'photographic color', Such as brown, would apparently be more acceptable than blue."

- Reginald Heron, Blueprint Into Blackprint

Afterimage, Dec. 1973, Volume 1, Number 3

Although the blue blueprint is the most stable and highly tonal form, there is still a groundswell away from its graphic blueness, especially among those intent upon using high-contrast, low-detail yielding transparencies. For those who find the blue distasteful, and for experimentalists, here are several processes for changing the blue into another, more "pleasing" color. Unfortunately the blueprint to blackprint process developed by Reg Heron and Henry Holmes Smith is too complex to reprint here (and indeed is too involved for most workers to even attempt; for those interested in this process, I refer you to the article and technical information in the Afterimage issue cited above.

Basically, the idea in these processes is to re-oxydize the ferric compound (by bleaching), and then to re-combine it with another organic substance (during a re-development) which thus produces another color. All of these processes call for a good well-processed blueprint with no varnish or other surface coating.

1. Greenish Black: This process uses for sulfuric acid and must be handled with extreme care; wear gloves and avoid contact!

• Mix solution of 70 grams Borax and 1000 cc water.

• Add, one drop at a time, sulfuric acid until solution will just redden litmus paper.

• Slowly add an ammonia solution diluted to 10% until litmus paper reading just begins to change from red color. If too much ammonia is added too quickly, add another drop or two of sulfuric acid to get back to red litmus reading and try again.

• Slowly, while agitating, add 10 grams of powdered catechu. Continue agitating or stirring until the catechu is dissolved.

• Filter the solution several times through 3 or 4 layers of muslin.

• Immerse blueprint in solution until it reaches desired color.

• Wash print in cool running water for 5 to 10 minutes.

2. Black: This seems to be the easiest of the color-changing processes, with reasonably safe and accessible chemicals.

• Immerse the print in a solution of Dektol (or a premixed solution of 250 cc ammonia and 1000 cc water - this amonia solution is smelly and noxious; the Dektol works just as well). The stronger the Dektol solution the more it will bleach the blue toward a goldenrod color which is nice in itself.

• When the blue is partly or entirely bleached out, rinse very briefly in running water, and then immerse it in a pre-mixed solution of 30 grams tannic acid and 1000 cc water; gradual redevelopment within 2-3 minutes in a smokey black color will occur.

• Wash for 3-5 minutes in running water.

• If the redeveloped "black" print is again contacted by Dektol or ammonia, a purplish-red color will occur.

3. Purple-Brown: Although this process is relatively easy, pyrogallic is expensive and hard to buy in small quantities.

• Mix a hot solution of 70 grams of tannic acid and 1000 cc water.

• Add just a trace of pyrogallic acid.

• Immerse the print until the blue color changes into a lilac color, and then rinse briefly in running water.

• Immerse the print in a solution of 15 grams of caustic potash and 1000 cc water until the color becomes the desired purple-brown.

• Wash for 10 to 15 minutes.

NOTE: This process should be completed as quickly as possible, otherwise the highlights could mottle. Also, if you like the light lilac color, the process can be ended after the first color change by simply washing for 10 to 15 minutes.

4. Violet-Black: Here again, the gallic acid, as well as the pyrogallic acid, is expensive and difficult to buy in small amounts.

• Mix a solution of 50 grams of sodium carbonate (crystal) and 1000 cc water.

• Immerse the print until it bleaches entirely to yellow.

• Rinse briefly in running water.

• Immerse print in a solution of 8 grams of gallic acid, .5 grams of pyrogallic acid, and 1000 cc of water until the desired coloration is reached.

• Wash in running water for 5 to 10 minutes.

Note: With gallic acid alone in the developing solution, purer violet tones are produced; by increasing the proportion of pyrogallic acid in the normal developing solution just slightly, a blacker coloration will result.