Unlike the silver print process, platinum lies on the paper surface, while silver lies in a gelatin or albumen emulsion that coats the paper. As a result, since no gelatin emulsion is used, the final platinum image is absolutely matte with a deposit of platinum (and/or palladium, its sister element which is also used in most platinum photographs) absorbed slightly into the paper.
In 1832 Englishmen Sir John Herschel and Robert Hunt conducted their own experiments, further refining the chemistry of the process. In 1844, in his book Researches on Light, Hunt recorded the first known description of anyone employing platinum to make a photographic print. However, although he tried several different combinations of chemicals with platinum, none of them succeeded in producing any permanency in the image. All of his prints faded after several months.
Over the next decade, Hunt noted that platinum prints he had left in the dark faded very slowly but gradually were restored to their original density. They eventually became permanent and, even more interesting, they shifted from a negative to a positive image.
By the early 1850s, however, other more reliable photographic processes, such as salt and albumen printing, had been developed and were beginning to be widely used. Those scientists who had previously conducted research on platinum lost interest in the process as other methods became more commercially viable. The only major advances in platinum research reported during that decade were made independently by C.J. Burnett and Lyonel Clark of Great Britain. In 1859 Burnett published an article in the British Journal of Photography describing his use of sodium chloroplatinate as a fixing agent. His modification of the platinum printing process resulted in prints that were reasonably permanent enough that he could exhibit them in public. That same year Clark also exhibited prints made using a slightly different process.
No notable advances were made during the 1860s, no doubt due to the rapid rise in the popularity of other processes. It was 1873 before the first patent for a platinotype process was granted, to William Willis (British Patent No. 2011, June 8, 1873). Willis introduced the "hot bath" method where a mixture of ferric oxalate and potassium chloroplatinite are coated onto paper which is then exposed through a negative and developed in a warm solution of potassium oxalate. This is the basic platinotype process which is in use today. In 1878 Willis was granted a second patent for a simplification of his initial process that eliminated the need for a hyposulfate bath. Two years later he received a third patent for further refinements to the process.
While Willis had greatly advanced the chemistry of the platinum process, by 1880 there was still no reliable method for the individual preparation of platinum paper. Two years later two Austrian Army offices, Giuseppe Pizzighelli and Arthur Baron V. Hubl, published a dissertation describing a straightforward process for preparing the paper. They continued their research for several years, and in 1887 Pizzighelli patented a new process that made the commercial production of platinum paper viable for the first time. The new process was briefly known as a "Pizzitype" and was marketed under the name "Dr. Jacoby's Printing Out Paper."
Willis quickly countered this advance by obtaining two more patents in 1888 for cold-bath processes. By adding more platinum to the developing process, he produced prints that had dense brown-black shadows rather than the lighter browns that were the best previous processes could produce. While much more aesthetically pleasing, prints developed by this process were difficult to reliably produce.
Four years later he began manufacturing a platinum paper that was designed for the cold-bath process, and this became the standard for the rest of the decade. The business he started in 1880, called the Patinotype Company, rapidly expanded, and soon he was selling his paper throughout Europe and in the United States By 1906 his company had sales totaling US $273,715, a significant amount at that time.
Seeing the skyrocketing demand for platinum paper, the Eastman Kodak Company in Rochester, New York, tried to develop its own line of paper starting in 1901, but they could not duplicate the quality of Willis' product. Kodak then tried to buy Willis' company, but he was not interested. Rebuffed, Kodak instead bought the relatively new company of Joseph Di Nunzio in Boston. Di Nunzio had developed a reasonably good platinum paper, which he sold under the name of "Angelo", and Kodak sold this paper for several years.
When Willis began marketing his paper platinum was relatively cheap, by 1907 platinum had become 52 times more expensive than silver. Eastman Kodak and most other producers stopped fabrication of the paper in 1916. Russia controlled 90% of the world platinum supply in World War I and all available platinum was used in the war effort.
Due to the shortage of commercial paper and high cost, photographers experimented with palladium paper and platinum-palladium mixes. Platinum paper has continued in use until the present, interrupted only by the world wars.
By varying the amount of platinum vs 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, adding additional "cachet" to a platinum print. The inherent low sensitivity of the process is because the ferric oxalate is sensitive to ultra-violet 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, rag, and rice, among others - even silk. On the collecting market, platinum prints often sell for many times what a similar silver-gelatin print would sell for.