Rangefinder Magazine
October 2005

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Platinum and Palladium Printing by Dick Arentz
How-to Excerpt from Paltinum and Palladium Printing, 2nd Edition (Focal Press, 2005)

Today’s platinum printers practice it as it was originally described in 1872—a hands-on printmaking process. The finished hand-coated platinum/palladium (Pt/Pd) print consists of pure platinum and/or palladium metal imbedded upon and inside the paper at a considerably greater thickness than can be laid on the surface by machine. A well-made platinum or palladium print excels in the delicacy of the tonal scale, image color and depth. Papers of different texture, hue and weight can be used, so interpretation is not limited to the dictates of a uniformly manufactured product.

Depending on available techniques, the print color of a platinum/palladium print can range from neutral gray to sepia. The mid-tones, rather than being compressed as they may be with modern silver paper, are evenly distributed, allowing for great subtlety in print values. Pure palladium, particularly, captures the nuances of the midto high-tones. It is frequently possible to print brilliant highlights directly, while still maintaining texture.

As one of the most permanent of photographic processes, platinum is also one of the most environmentally safe. The chemicals used are relatively inert metals, common cations (sodium and potassium), iron oxalates (rust) and weak acids. The oxidizing compounds, while hazardous, are used in infinitesimal quantities.

As it is a contact-printing process, if enlargement is desired, it must be done through photomechanical or digital means.

The Process

The In-camera Negative: The negative for contact printing with Pt/Pd should have about one third more contrast than one used for silver gelatin paper. For example, while an “ideal” negative for silver may read 1.3 – .3 = 1.0, a negative for Pt/ Pd printing is best when the density range is in the range of 1.4 (1.7 – .3 = 1.4).

The Digitally Enlarged Negative: Recently, one of the great advances in Pt/Pd printing has been the perfection of the digitally generated negative. Although space does not allow a complete discussion, using Mark Nelson’s process (www.precision digitalnegatives.com/), I have come to the conclusion that a print can be made by this process that rivals one made from the traditional in-camera negative. However, digitalization is not a shortcut to eliminating either the well seen, exposed and developed image or the mastery of Pt/Pd printing technique. In a sense, it is additive, in that a third set of skills is necessary for the making of a successful Pt/Pd print.

The Light Source

Intense ultraviolet (UV) light in the 200–400 nanometer range is needed. The sun was the first source of light for all of the 19th century photographic printing process and is used by many contemporary Pt/Pd printers, sandwiching the negative and paper in a printing frame. However, for the more serious worker, the sun’s UV light is unpredictable. Now, there are many choices of UV light sources, including banks of UV fluorescent tubes (Figure 1) and mercury vapor or metal halide machines. Some of the “plate burners” come with a vacuum easel.

Coating Agent

Salts of platinum and/or palladium combined with a solution of ferric oxalate are used to coat the paper. The ferric oxalate is the sensitizer, as UV light affects the structure of the iron (ferric) element to cause a reduction of the platinum or palladium salt to pure metal. The process of development in any number of weak organic solutions causes an immediate coalescing of the metal particles to produce an instant image. At that point the unwanted salts are dissolved and removed. This process is completed with the use of clearing baths.

Contrast Control

An infinitesimal amount of an oxidizer (restrainer) is either added to the coating agent or put in the developer. Increased amounts of oxidizer will shorten the paper contrast. (Just as going from Grade 1 to Grade 4 silver gelatin paper.) Historically, oxidizers containing chlorates or dichromates have been used. Now an exciting new compound is the choice of many palladium printers. It is a platinum salt, sodium chloroplatinate, called Na2. Na2 is a form of platinum that does not form the image. It can only be usd to control contrast with pure palladium

Coating of the Paper

The liquid coating agent can be applied either with a brush or a coating rod. Camel hair or Haki brushes are best for smaller prints (Figure 2).

Brushes

With most papers, regardless of how well sized, a water spot will form around the stagnant solution a few seconds after the solution contacts the paper. Therefore, it is essential that the solution be dispersed, however imperfectly, as quickly as possible. After the borders have been reached, the coating can be refined. Put the liquid in a beaker or plastic cup. Inspect the brush for any particles or loose bristles. Examine the paper surface, blowing off any dust. If there is a defect, discard the paper. Holding the brush in your working hand, pour the entire solution, forming a bead in the center of the coating area (Figures 3 and 4). Immediately, sweep the material in all directions with the brush until a film covers the entire coating area.

Take a cotton applicator in the other hand. Now, using only the weight of the brush, slowly pass it across the image. If a particle or free bristle appears, lightly take a swipe at it with the cotton applicator. If unsuccessful after two tries, quit. Otherwise, the cotton applicator will readily mark the softening paper nap. The particle can be dealt with later, after drying, by flicking it off with a razor blade. If that does not work, don’t dig a hole in the paper; it can likely be covered during spotting. To decrease the chances of this occurring, take care not to shake or stir up the bottle of metal salt.

Coating Rods

Various forms of glass rods were available in the past; now, some have been produced with a handle, facilitating ease of coating. A number are available, including the Puddle Pusher®, which comes in sizes from 4.5 to 12 inches (Figure 5).

The length of rod should be slightly more than the width of your coating area. The coating rod requires practice. It is not applicable for all papers, so do some tests using only sensitizer. The thinner papers may wrinkle too soon to allow sufficient passes with the rod. A sheet of plate glass that is completely level is required as a coating surface. The emulsion is best “injected” under the rod with a hypodermic syringe.

Determine how much solution is necessary. Generally the rod will require only two thirds the amount needed for a brush. Draw it into a syringe of appropriate size. Do not use the needle. Have a cotton applicator handy. If you are right-handed, balance the rod on the left side just outside of the coating area. Stabilize the rod with your left hand while you inject a bead of liquid along the contact area between the rod and paper (Figure 6). It should be thoroughly drawn in to create a continuous film between the rod and paper along the width of the coating area. Now, using the right hand, manipulate the rod so the volume of material (which should be a continuous bead) is still in contact with the rod but adjacent to the coating area. With slight pressure, draw the bead slowly across the coating area (Figure 7). If done properly, the paper should be completely coated. There should now be a bead on the other side. “Capture” it by repositioning the rod, and slowly draw it to the other side (Figure 8). If bare areas remain, it may be necessary to draw the material vertically across the image area. This is best avoided.

You will note that the paper soon begins to wrinkle. This is the time to stop. Sop up the excess solution at the edges with a cotton applicator. Do not attempt to introduce it into the image.

Drying

Allow the coating to air dry two to five minutes before drying with heat. Using a hair dryer at medium settings, or a drying apparatus, blow dry both sides (Figure 9) in a well-ventilated area. Use the blow dryer at eight to 12 inches. The coating should become light orange (Pt/Pd) to orange (Pd). Be careful not to burn the paper. Examine the dry coating with a dim light. Any spots or bristles can be scratched away using a single-edged razor blade. Metal precipitant generally cannot be removed. Save it for spotting.

Exposure

Sandwich the paper and the negative in the printing frame. Handle the negative with cotton gloves. Use compressed air or an air syringe to clean the glass of the printing frame and to dust off the negative. Check the contact of negative and paper in the printing frame before placing under UV light (Figure 10). While looking through the glass, squeeze the center of the back. If you see movement, the contact is bad. To remedy the problem add layers of felt between the paper and the back. Set a timer for the determined time and expose the print. (Figure 11) While this is occurring, you can begin to heat the developer and clean up. As stated, if you use a commercial plate burner, most likely it will have a vacuum easel (Figure 12).

After exposure, you will see a printingout image (Figure 13). Quickly slide the print into preheated developer at 90°F. (Most Pt/Pd printers use potassium oxalate for warm tones and ammonium citrate for neutral tones.) Another method is to place the print face up in the dry tray and rapidly pour the developer over it. Development will be instantaneous (Figure 14). Any portion of the print not receiving immediate development will permanently streak. Never develop a print face down.

Develop, with constant agitation, for 11/2 to 2 minutes. Then lift the print by grasping generous parts of two corners and allow it to drain into the developer tray. (Take care with tongs; you may tear off a corner.)

The Clearing Baths

Three working solutions of hypo clearing agent are usually used. Place the print directly into the first clearing bath. Clear for five minutes with constant agitation (Figure 15). Clearing in the second and third baths will also be 5 minutes each. As the paper becomes soaked, more care is needed in transferring it to avoid tearing. When the first bath becomes cloudy, empty it and move the second and third baths over. Replace the first clearing tray with new solution, now making it the third bath. For an exhibition-quality print, the last bath should always be completely clear. The final step is a 15 to 30 minute wash in running water. Either a hose or siphon can be used. After washing, place the print, face up, on a clean blotter or drying screen.