Fred Endsley

BLUEPRINTS, CYANOTYPES, FERROPRUSSIATES, AND IRON PRINTS

". . . and there is the simple blueprint, which survives, as the Darwinians tell us some of the lower forms of life survive, from the extreme simplicity of its structure."

- R.C. Bayley (1935)

The blueprint process is the longest living photographic process still in common use. The earliest record that we have of the blueprint process are some research notes dated February 13, 1839 of Sir John Herschel, who formally announced it to the Royal Photographic Society of England three years later in June 1842. Only Niepce's process that led to the first photograph has survived longer, and its use has been solely restricted to the graphic arts, never having been used as a purely photographic process.

Herschel's only real application of the cyanotype was to make copies of his notes that he did not want to trust to the inaccuracies of hand transcription. He simply placed his notes over a sheet of blueprint coated paper and exposed through the handwriting by sunlight, thus creating the first photo-copy method.

Until the 20th century however, aside from the copying of plans, blueprinting found little serious commercial application. For many years after its discovery blueprinting was used mostly for very limited graphic copying, photogram illustrations, and proof-printing. Gernsheim cites an entire unique book, Photographs of British Algae: Cyanotype Impressions, published in sections in the 1840's by Anna Atkins, that was illustrated by 411 original blueprints of seaweeds (certainly a much more accurate method for the time than hand drawing them). Blueprinting was also used during a siege in the Boer War when Lt. Col. Baden-Powell had a local photographer make a relatively large edition of blueprinted stamps and money because no other printing process was available. It was also quickly discovered that blueprint emulsion worked well on cloth, and commercially- sensitized cyanotype fabric was easily available in bolts by mail-order. At the turn of the century, blueprinting was used to make quick copies of frequently changed documents such as menus and inventory sheets. During the same period it was used by photo journalists, such as Charles Loomis, in the exploration and development of the West, because of its stability, ease of mixing and processing, and low-cost in conditions when other photographic methods were impractical.

However, when commercial silver materials became accessible and practical, and with the advent of more sophisticated copying systems (offset, xerox, etc.), the blueprint was relegated almost entirely to large-format mechanical reproduction of architectural plans. Although its major use today continues to reside in the blueprint houses, in-depth work by such people as Robert Fichter, Bobbi Carey, Darryl Curran led to a renewed awareness in the creative possibilities of the blueprint.

The blueprint is a member of the family of iron salt processes that include the kallitype, the palladium print, and the platinotype which are considered by many to be the aristocracy of photographic printing processes. Relatively low material expense, ease of manipulation over a variety of surfaces, good permanence, and a long tonal range continue to make the blueprint one of the most practical and attractive of most hand-applied emulsions.

Making a blueprint is quite simple. The basic premise is that all ferric salts become light sensitive in the presence of organic substances, Most recipes call for the surface to be coated with a light-sensitive mixture of an iron compound (today, ferric ammonium citrate is generally used) and potassium ferricyanide. Exposure to actinic (UV) light breaks the iron compound down into another state (oxidation) by releasing carbon in the form of carbonic acid. When the exposed print is then immersed in water, this new compound, peroxide iron salt (having been reduced by the actinic light), reacts with the potassium ferricyanide to form "Prussian blue" (ferroprussiate), a stable deep blue-colored compound.

Materials: Small, accurate graduate measuring individual cc's or ml's. Applicators: brushes (it's helpful to have a soft, wide one and a smaller, bright one, at least), small sponges, cloth squeegee, airbrush. Transparencies for contact printing.

Ground: paper that will hold up well in water, natural cloth (synthetics don't work well), wood, etc. Rubber gloves, small paper cups or dishes for mixing, a clean-up sponge, a non-porous working surface, a good gas mask, if applying with air brush.

NOTE: Although nearly all photographic chemicals are poisonous if ingested, OXALIC ACID IS A POISON WHICH CAN BE INGESTED DIRECTLY THROUGH YOU SKIN INTO YOUR BLOODSTREAM. If you use formulae containing it, wear rubber gloves, avoid excessive contact with it, and if spraying or airbrushing it on use a very efficient gas mask and wear goggles. If after very much contact with it you begin feeling ill, please stop; its not worth your health.

Formulary: Although there are numerous formulae (refer to Modern Heliographic Process, by Ernst Leitze), I am only supplying three of the simplest here (as derived from Herschel's original formula) which can be employed for slightly different purposes.

Formula I is the most primitive and commonly used (contains only two ingredients plus water), and retains maximum sensitivity in the bottle if stored well and uncontaminated for about 4 to 6 weeks. Formula II is used when a large quantity of emulsion is needed (for coating cloth etc.) and has a maximum sensitive life of about four hours. Formula III will last from 4 to 6 months, if stored well and uncontaminated.

Regardless of which formula is to be used, the solutions should be kept in well-stoppered dark bottles at a stable temperature. Do not pour contaminated solution back into bottles or exchange lids. Paper coated with any of these three emulsion formulas will retain maximum sensitivity for about two hours after it has been dried (less if high ambient humidity is present), after this the two main chemical ingredients begin to neutralize each other, thus reducing sensitivity.

Formula I:

Solution A

50 grams ferric ammonium citrate (Green Scales)
250 cc water (pref. distilled)

Solution B

35 grams potassium ferricyanide
250 cc water (pref. distilled)

Mix equal portions of A and B just before use.

Formula II:

Single Solution

1.25 grams oxalic acid
33.7 grams ferric ammonium citrate (Green Scales)
11.2 grams potassium ferricyanide
.25 grams ammonium dichromate
250 cc water (pref. distilled)

Mix altogether just before use.

Formula III:

Solution A

1.25 (20) grams oxalic acid
67.5 (1080) grams ferric ammonium citrate (Green Scales)
250 (4000) cc water (pref. distilled)

Solution B

1.25 (20) grams oxalic acid
22.5 (360) grams potassium ferricyanide
.5 (8) grams ammonium dichromate
250 (4000) cc water (pref. distilled)

Mix equal portions just before use.

Note: It takes about 20-30 cc of the total mixed blueprint emulsion to cover 600 square inches of paper (20" x 30 "); depending on the heaviness of the weave and the receptivity of the paper fibers; it takes about four times as much solution to cover the same area on cloth.

Procedure: Do all work under safelight (40-60 watt orange buglight will suffice).

If you intend to coat the blueprinted image again with another medium (e.g. gum print), and you want to keep both printings in good registration, pre-shrink the paper or cloth by soaking in hot water for 20 minutes and dry completely before applying any emulsion .

1. Apply solution onto desired surface. Because blueprint solution does not have a vehicle such as gum arabic or gelatine, it should be thought of as a dye which must be allowed to soak into the fibers of the ground (in some cases it must actually be worked in); it will not work well over sizing or into polyester. The solution should be coated evenly, unless you desire a mottled image appearance. A wide, soft brush, sponge, or squeegee seems the most efficient, when possible, for this purpose. Care must be taken not to re-coat an area which has already begun to dry, as the oxidizing process will be interrupted and the emulsion will begin to develop and neutralize itself, thus losing sensitivity to exposure.

2. Hang up, or place on plastic screens, and allow to dry completely.

Drying is somewhat tricky, especially in humidity. The emulsion should not be exposed until it is completely dry (a hair dryer is handy for speeding up the process, but be careful not to get the emulsion hot); if exposed when still damp it will not only develop while exposing (thus negating the image), but also the potassium ferricyanide in the emulsion will bleach out the silver in your transparency. If allowed to sit too long after it is dry, the emulsion will lose sensitivity.

3. Once dry, expose under a transparency in a contact frame or under heavy enough glass to provide good contact. Another method for getting reasonably good transparency contact of pieces too large to make the use of glass practical is to spray the contact side of the transparency with a light coating of spray cement, thus enabling it to stick to the surface of the ground. Exposure times are dependent upon the density of the transparency, and the degree of contrast and deepness of the blue color that you desire. Generally though, times range from 4 to 10 minutes in direct sunlight, 30 to 60 minutes in open shade, 10 to 20 minutes under unshielded UV fluorescents, 5 to 15 minutes under high intensity arc lamp (Nuarc), 3 to 10 minutes under mercury vapor or pulse-xenon lamp, and 20 to 40 minutes under a pair of 500 watt photo floods or sunlamps. Exposures through paper negatives take 2 to 3 times as long. Exposures onto cloth or other low-reflective grounds should be about 50% longer for any given light source.

4. Develop for 10 to 15 minutes (cloth may take longer) face down in running water, or until the base is clear and the yellow-green stain has completely disappeared; if not completely cleared, the blueprint can still be affected and fogged by further exposure to actinic (UV) light.

5. Hang up, or place on plastic screen, to dry. The blue color should deepen about one "zone" with drying. Be careful not to pick up stains from dirty clothespins or screens.

Special Notes and Problems:

A. There is another somewhat more complicated method for coating and exposure which increases the sensitivity of the emulsion by 30 - 50%:

B. The blueprint image is soluble in alkaline solutions. If your tap water is too heavily alkaline, your image will begin to bleach out after about 10 minutes, or if you gum print over it, the successive washings could also fade it. Solutions:

C. Occasionally the yellow stain will not clear; in that case, try a quick rinse in a 1:10 Dektol solution followed by a 5 to 10 minute wash. Well-diluted household ammonia also is a very controllable bleaching agent which can produce nicely colored results.

D. Blueprints on clothing need to be washed in a very gentle, non-alkaline/non-phosphate detergent, and preferably soft water; otherwise fading occurs quickly. Woolite and handwashing help greatly to prolong the life of blueprint-cloths that get washed often.


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