|
Platinum prints, also called ''platinotypes'', are photographic prints made by a monochrome printing process that provides the greatest tonal range of any printing method using chemical development. Platinum prints are made by photographers and favored by collectors because of their tonal range, the surface quality and their permanence. A platinum print provides a broad scale of tones from black to white. The platinum tones range from warm black, to reddish brown, to expanded mid-tone grays that are unobtainable in silver prints.〔 〕 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. Platinum prints are the most durable of all photographic processes. The platinum group metals are very stable against chemical reactions that might degrade the print—even more stable than gold. It is estimated that a platinum image, properly made, can last thousands of years.〔 Some of the desirable characteristics of a platinum print include: * The reflective quality of the print is much more diffuse in nature compared to glossy prints that typically have specular reflections. * A very delicate, large tonal range. * Not being coated with gelatin, the prints do not exhibit the tendency to curl. * The darkest possible tones in the prints are lighter than silver-based prints. Recent studies have attributed this to an optical illusion produced by the gelatin coating on RC and fiber-based papers. However, platinotypes that have been waxed or varnished will produce images that appear to have greater D-max than silver prints. * A greatly decreased susceptibility to deterioration compared to silver-based prints due to the inherent stability of the process and also because they are commonly printed on 100% rag papers. Many practitioners have abandoned platinum and only use palladium. The process using palladium alone (sodium tetrachloropalladate) is similar to standard processes, but rather than using ferric oxalate plus potassium chlorate as the restrainer (which is ineffective for palladium), a weak solution of sodium chloroplatinate is used instead. Sodium chloroplatinate, in contrast to potassium chlorate, does not cause grain. This formula is generally referred to as the ''Na2 method''. This somewhat misleading abbreviation was coined by Richard Sullivan of Bostick & Sullivan, one of the principal suppliers of chemistry and printing supplies, who popularized the process. ==History== The first person to have recorded observing the action of light rays on platinum was Ferdinand Gehlen of Germany in 1830. The following year his countryman Johann Wolfgang Dobereiner determined that the action of light on platinum was quite weak, but that perhaps something could be combined with platinum to increase its sensitivity. Through experimenting, he eventually found that ferric oxalate was a highly-effective enhancer. The combination of these two metals remains the basis of the platinotype process in use today.〔John Hafey & Tom Shillea. (The Platinum Print & The History of the Platinum Process ). kimeia.com〕 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 resumed their original density, and interestingly had also shifted from a negative to a positive image, eventually becoming permanent.〔 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 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 chloroplatinate 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 officers, 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 that previous processes could produce. While much more aesthetically pleasing, prints developed by this process were difficult to produce reliably. 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 Platinotype 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 $273,715 ($ in 2009 dollars), 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's product. Kodak then tried to buy Willis's 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. Nevertheless, platinum paper has continued in use until the present, interrupted only by the world wars. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Platinum print」の詳細全文を読む スポンサード リンク
|