Instead of ordering the sensitizing solutions already mixed, I opted to order the dry chemicals to insure freshness. By doing so I could mix smaller batches for the printing at hand, and all printings could use freshly mixed chemicals. Some experiments published by Bostick & Sullivan suggest that the sensitizing solutions begin to deteriorate quickly once mixed.

The proportions of dry chemicals were measured on a triple beam balance. However because the amount of potassium chlorate to be included in the "contrast" sensitizer was only 0.3 gm., a percentage solution was prepared to insure enough precision in measurement. The percentage solution was made by diluting 6 gm. in 500 ml. of water, and using 25 ml. of the water/chlorate solution to dissolve 6.75 gm. of ferric oxalate powder and 0.5 gm. of oxalic acid. Distilled water was used always to avoid problems with minerals dissolved in tap water. The ferric oxalate dissolves slowly, usually taking overnight. Excess chlorate solution was discarded because its cost was low and it deteriorates rapidly. Most chemical dilutions were prepared using the recommendations in Bostick & Sullivan's Labnotes (very informative-well worth the price!) and B&S's Lumen journals. Bostick & Sullivan offers a very good supply of information that is useful to the platinum/palladium printer. These are highly recommended for those wanting to use modern, non-toxic printing materials. Most older references present obsolete and dangerous methods that B&S has replaced. Very good information and how-to tips are abundant. B&S's prices for chemicals are also much lower than Photographer's Formulary prices.

The platinum/palladium ratio that I used for best color was 1/3 platinum and 2/3 palladium. Pure palladium was too yellow-warm for my tastes. Color was also affected by paper choice.

The paper that I prefer for the process is Strathmore's 2-ply Bristol, which is available in the student store. It has a plate finish that does not absorb much solution, making spreading of the sensitizers easy. Also it makes a sharp image because of the smooth surface. It separates into two "plys" in the final wash, but that did not cause a problem. The leftover ply is simply discarded. The paper has a very nice white color, not too bluish and not too yellow.

Another paper of promise was Strathmore 500 series drawing paper, although attempts at locating it were unsuccessful. Strathmore's 400 series paper was awful. It tore easily when wet, and did not develop a good black. Arches Cover from Light Impressions was tried, but it had very small white specks in the dark tones. Arnold Gassan thought that it might be caused by small ferrous particles imbedded in the paper. The particles would de-sensitize the solutions.

Coating of the paper was carried out in a room illuminated with a yellow "bug light". A Japanese brush, without metal, was used to coat the paper with sensitizer. It was found that the Strathmore Bristol paper required vigorous brushing of the sensitizer to achieve a good coating. A circular brushing pattern was used for a minute or so after the sensitizer was first spread on using the more traditional right-angle brush pattern. The application could almost be described as "scrubbing" the sensitizer into the hard surface of this paper. Other papers tend to abrade with as much brushing, but the Strathmore has a very hard, smooth surface that requires it. A delay between the time the paper was coated and dried with a hair dryer allowed the sensitizer to penetrate the surface of the paper for good adhesion.

Exposure was provided by a bank of 2 foot long fluorescent lights mounted in 3 two-bulb fixtures. Sylvania 350 BL lights were used- these do not have the purple coating that the usual blacklights have. Exposures usually ran about 6-12 min. for average negatives.

The developer used was non-toxic ammonium citrate as packaged from Bostick & Sullivan. Development was immediate, but prints were agitated in the developer for 1 full minute. I found that the common method of pouring the developer onto the print in the tray provided poor evenness. Lines of uneven density formed where the developer hit first and no amount of subsequent development would eliminate the marks. I eventually found that uniform density was best achieved by pouring the developer into the tray first, and smoothly immersing the print upside down into the developer. Air bells would sometimes appear if the developer became viscous because of excessive evaporation between prints. The air bells would not disappear after full development so they should be avoided. Mixing some new developer with the old keeps the viscosity at a desireable level and reduces the tendency for air bell formation. Because developer is so much cheaper than the precious metals, it is unwise to extend the developer usage beyond its limit. Developer temperature was maintained at 110-120 deg. F. except as noted below. A "hot pot" type of kitchen soup warmer was used to warm the developer between prints. Because the warmer had an aluminum bottom, it was used merely as a warm water bath for a plastic container that held the developer solution. This usage avoided potentially adverse metal/developer contact.

One unusual aspect of platinum/palladium printing was that more exposure combined with development in a cooler solution (80 deg.) produced more contrast. It is backwards from experiences with silver.

Prints were then placed in 3 successive clearing baths made from non-toxic EDTA. Measurements were not exact, but about 2 tablespoons of EDTA powder were used in each liter of clearing bath. The first bath gets discarded after several 8x10 prints were cleared, and the second bath becomes the first, etc. The prints were immersed in the baths for 5 min. each bath. A water rinse was used between each bath to extend the effectiveness of the solutions.

Washing required care to prevent abrasion of the delicate paper surface. Abrasion caused little fibers of paper to lose their coating of platinum with a resulting grainy appearance to the print. With the short times used for test strips, no abrasion was apparent. However when trying to insure that all harmful chemicals were washed out after making a good print, I have had some problems with abrasion. Strongly directed water jets should be avoided. Wash times were 30 min. for good prints.

It should be noted that the formula listed in The Keepers of Light for the palladium solution is incorrect. Use 55 ml. of water instead of 40. This is one of the handy tidbits that makes Bostick & Sullivan so valuable as an information source.

Sensitizer Solution for Contrast Control
With Platinum/Palladium

Solution 1: 6.75 gm. Ferric Oxalate + 0.5 gm. Oxalic Acid, dissolve in 25 ml. distilled water.

Solution 2: 6.75 gm. Ferric Oxalate + 0.5 gm. Oxalic Acid, dissolve in 25 ml. of Potassium Chlorate solution. Potassium Chlorate solution is made by dissolving 3 gm. Pot. Chlorate in 250 ml. water. Discard the excess; it won't keep.

Solution 3: Either Platinum or Palladium solution as mixed below:

Palladium: 3.75 gm. Sodium Chloropalladite dissolved in 25 ml. distilled water at 38 deg. C. (100 F.)

Platinum: 5 gm. Potassium Chloroplatinite dissolved in 25 ml. distilled water at 38 deg. C. (100 F.)

NOTE: Oxalic acid in Solution 1 & 2 is probably not required. WRS 4/7/91

SALTED PAPER PROCESS:
The best paper for salted paper was again found to be Strathmore 2-ply from the student store. The hard finish was necessary to prevent all the silver nitrate sensitizing solution from sinking into the paper and greatly reducing contrast. The paper must be well sized also with the salting solution. The formula in the Keeper's book was used to prepare the salting and sensitizing solutions, with the exception of adding more gelatin to the salting solution. Keeper's called for:

water 280 ml.

gelatin 2 gm.

sodium citrate 6 gm.

ammonium chloride 6 gm.

I used 3 gm. of gelatin instead to provide more sizing. The process steps followed were those in the Keepers of the Light, so it would be redundant to repeat them here.

First prints lacked D-Max and contrast. It was found to be an insufficient supply of silver nitrate solution at the surface of the paper. It all sank into the paper at first, causing the poor appearance. The prints made with more gelatin and the hard, smooth Strathmore paper looked much better. The silver nitrate remained on the surface longer when brushing on, producing a full, even coat. About 30 drops of Silver Nitrate covered an 8x10 with plenty to spare. Exposure times were very long, running close to an hour for one contrasty negative. Print appearance was not as nice as the platinum process- shadows lacked detail and contrast. The process would work best with negatives having mostly highlight detail. Some bugs remain in the process for me. A splotchy mottled appearance is apparent. A double or triple coating of salting solution should be tried, perhaps with a formalin hardening step between coats of gelatin/salting solution to "set" the already applied gelatin layer(s).

The prints appeared to have a satisfactory warm purple color after fixing with plain hypo and "heat toning" in a dry mount press. Toning with gold was tried. Gold toning with the Borax toning formula detailed in Keepers of the Light made the prints cooler (bluer). Because of the high cost of gold, some experiments would be in order to find a toner formula that lasts more than a few hours before it decays. I rather prefer the color of the merely heat toned prints without any chemical toner. Selenium toning was tried, but the print lost density and practically faded away.

A side experiment was tried with the salted paper process. Because enlarging papers are not radically different chemically, I placed a piece of lightly exposed salted paper in Dektol, and immediately it turned black. Several experiments followed to try to make a faster paper from the salted paper by using development after exposure. However, the paper always turned black in the developer, even when it had received no exposure to white light. (Darkroom safelights were used during coating and drying.) In one experiment, the coated paper was rinsed in water after it was sensitized to remove excess silver nitrate. After drying, it still turned dark without exposure when placed in Dektol. The experiments to make enlarging speed paper were considered unsuccessful.

PRINTING FRAME
I found that the commercial printing frames sold today are unsatisfactory for optimum results. First tried was a Gravity Works unit of about 16x20 size. The specifications state that the "glass" is actually a UV transmitting type of Plexiglas. Because most of the alternative processes use UV light as the primary exposing radiation, this sounded appealing. However the unit was not capable of holding the negative in close contact with the printing paper, causing unsharp images. A 8x10 Premier brand printing frame was next tried with similar unsharp results. Each of these printing frames was modified in an attempt to make them work. A spacer was placed between the elastic strap of the Gravity Works frame to put more pressure between the backing and the Plexiglas. A felt pad was glued onto the Premier frame to more uniformly distribute the clamping forces, but these fixes were unsuccessful.

The best solution found was also the cheapest. Two pieces of 11x14 plate glass with ground edges were obtained from a glass store and hinged together with electrical tape along one edge. Some sponge rubber feet were glued onto the bottom to make handling easier. The print and negative were placed between the two glass plates for subsequent exposure. Tests showed that the 1/4 inch thick plate glass provided nearly identical print times as the so-called UV transmitting Plexiglas in the Gravity Works unit. The actinic radiation must pass through the glass as easily as through the more expensive, flexible, scratch prone Plexiglas. The sharpness provided by the two very flat panes of glass was much better than the commercial print frames. The homemade print frame is vastly superior to the commercial versions, and is highly recommended.

ENLARGING NEGATIVES
Most of the prints made to date have been from enlarged negatives. I used Kodak's Professional Direct Duplicating Film for making enlarged negatives. However obtaining this scarce film provided some delays. The film was ordered from Light Impressions in December with delivery promised within 10 days. Unfortunately, the film didn't arrive until the following March. This is an excessive delay, and Light Impressions was not helpful after the order was placed. It would be wise to find another supplier of this film. Calumet in Chicago might be a potential source.

Although Kodak states that the film can be developed in Dektol, I found that the characteristic curve was very S-shaped. Because a straight line would best duplicate the tones of the original negative, I experimented with various developers to find a better curve. Because Arnold Gassan suggested that one former student had very good luck with Buetler A & B developer, I used that as a starting point. I found that the Buetler was much too inactive to provide desired density in the duplicate negative, so it was modified with additions of Zone VI print developer. Because the Zone VI print developer contained Hydroquinone, it performed as a percentage solution of contrast enhancing Hydroquinone. Some Potassium Bromide was then needed to reduce fog, but the result was a more favorable characteristic curve for reproducing the tones of the original negative.

The developer formula is given below:

Buetler "A" 300 ml.

Buetler "B" 1700 ml.

Zone VI Print Dev. Stock Solution 50 ml

Potassium Bromide 10% Solution 15 ml.

Water 2000 ml.

The film was developed in stainless steel hangers for 5 minutes at 73 deg. with continuous agitation. Times for other negatives may vary according to the density of the original negative as well as for personal preferences for the final print.

One note of caution about the Duplicating film should be related. The film arrived fresh in March and was stored in my darkroom over a hot summer. When the film was used again in the fall, it had fogged adjacent the opened edge of the foil packet. Apparently the warm temperatures combined with the air near the edge caused a local deterioration of the film. Kodak's warning to keep this film refrigerated should be heeded.

William R. Schneider
March 8, 1988
Revised May 30, 1990
2^nd Revision April 7, 1991
3^rd Revision March 30, 2000 to update address of Bostick and Sullivan