Editing Platinum print (section)

==Chemistry==
Platinum printing is based on the [[Photochemistry|light sensitivity]] of [[ferric oxalate]]. Ferric oxalate is reduced to [[ferrous oxalate]] by [[UV-light]]. The ferrous oxalate then reacts with platinum(II) or palladium(II) reducing it to elemental platinum (or palladium), which builds up the image.

By varying the amount of platinum versus palladium and the addition of oxidizing chemicals such as [[hydrogen peroxide]] and [[potassium dichromate]] or [[potassium chlorate]], the contrast and "color" of the final image can be modified. Because of the non-uniformity of the coating and mixing phases of the process, no two prints are exactly the same.

In 2002, working from research done by Howard Efner and Richard Sullivan, Dick Arentz formulated the methodology for using sodium chloroplatinate as a contrast control agent. Richard Sullivan coined the term Na2 and began to sell a 20% solution through Bostick and Sullivan. Arentz found that, since it is a platinum compound (sodium chloroplatinATE), it does not work with platinum prints (potassium chloroplatinITE). It does, however, shorten the scale of a pure palladium print. When minute quantities of sodium chloroplatinate are added to the palladium salt/ferric oxalate emulsion it produces the high-contrast prints needed for thin negatives, but does not exhibit the granularity found when using traditional chlorates. A palladium print made with potassium chlorate will take on a warm, sepia tone. The same print using sodium chloroplatinate will have cooler tones similar to those of a platinum/palladium print.
 
The inherent low sensitivity of the process occurs because the ferric oxalate is sensitive to [[ultraviolet light]] only, thus specialized light sources must be used and exposure times are many times greater than those used in silver-based photographic processes.
 
Due to the unavailability of pre-coated sensitized paper, all platinum/palladium printing is done on paper coated by the printer. The light sensitive chemicals are mixed from powdered basic chemicals, or some commercially available solutions, then hand applied with a brush or a cylindrical "pusher".
 
Many artists achieve varying effects by choosing different papers for different surface characteristics, including [[vellum]], 100% cotton rag, silk, and rice, among others. On the collecting market, platinum prints often sell for many times what a similar silver-gelatin print would bring.