THE PLATINO-PALLADIOTYPE

 PRINTING PROCESSES.

Prologue

"I do not profess to have perfected an art but to have commenced one, the limits of which it is not possible at present exactly to ascertain. I only claim to have based this art on a secure foundation" (Henry Fox Talbot)

These words, written in 1839, demonstrate the remarkable foresight and vision of Henry Fox Talbot, considered by most authorities to have been responsible for developing the first practical photographic process. Although it had been known for centuries that the physical properties of some materials appeared to change when exposed to strong sunlight, it wasn’t until the early years of the 19^th Century that the principle behind the phenomenon of photosensitivity began to be widely understood. In the space of two decades, a series of largely simultaneous – but distinct – scientific experimentations in England and Continental Europe precipitated in the identification of a variety of techniques that could successfully harness and exploit the potential of photochemical reactions and apply them to photographic imaging.

On the 31^st January 1839, Fox Talbot presented his discovery to the Royal Society in London entitled: "Some account of the Art of Photogenic drawing, or the process by which natural objects may be made to delineate themselves without the aid of the artist's pencil." He called his process the Calotype (from the Greek Kalos: meaning beautiful) and in 1844, he published the ‘The Pencil of Nature’ the first book in the world to be sold with photographic illustrations. Although the Calotype did not survive, the fundamental concept of creating a negative from which any number of positive prints can subsequently made, ultimately served to underpin the evolution of photographic imagery for generations: a legacy that lies at the heart of practically every photograph produced prior to the dawn of digital imaging.

In the years that have passed since Fox Talbot’s revelation, photographic science has employed many different forms of physical expression. Some proved ephemeral, if not in the literal sense, then certainly in the historical context, and only fleetingly appeared before the inexorable march of scientific experimentation evolved developments that condemned them to obscurity; destined to serve out existence in the pages of dusty photographic almanacs. Others lived on, perhaps for decades, only to suffer a more mundane and protracted decline, often atrophy through unfavourable economics.

Ultimately, the almost constant flux of discovery and innovation subsided and the practicalities and economics of commercialism allied to the evolution of viable image permanence satisfied the aesthetic and creative aspirations of the art through the medium of silver halide based printing papers: enduring for almost a century before the preponderance of digital technology ushered in the dawn of a new photo-imaging epoch.

But of all of the printing techniques; from Fox Talbot’s Calotype / Salt Print, through the various incarnations of Albumen prints, Collodion prints, Carbon prints, the ubiquitous silver halide emulsion to the latest digital imaging techniques, one process stands above them all: the Platinum / Palladium print.

The History of the Platino-Palladiotype Process

The Platinum/Palladium print stands at the summit of all of the monochrome printing processes. Although the process can be traced back to early nineteenth century England (Sir John Herschel had demonstrated the photosensitive properties of Platinum salts in the presence of certain organic compounds in the early 1830’s), the first workable platinum process didn’t appear until 1873 when William Willis patented his Platinotype process.

For several decades, his Platinotype Company sold pre-coated Platinum papers that became the pre-eminent printing material for the most discerning photographers of the late Victorian/early Edwardian era. An indication of the popularity that this process enjoyed at this time can be found in statistics that reveal that almost 50% of the prints on show at the 1894 Photographic Society Exhibition in London were Platinotypes.

By 1907 however, platinum had become over fifty times more expensive than silver, and despite attempts to make the process more commercially viable by mixing the slightly cheaper palladium to the sensitizer, the outbreak of the First World War in 1914 meant that these precious metals had other, more military uses, and the process effectively atrophied. 

The Platinotype process enjoyed a renaissance in the 1970’s and 1980’s, most notably in America, and remains fundamentally unchanged to this day although a great deal of credit must go to Dr Mike Ware who is based in Buxton, England for developing a more benign and user friendly set of chemistry which has done much further the Platino-Palladiotype’s popularity.

The Physical Properties of Platinum and Palladium

Both platinum and palladium are extremely rare, precious metals that belong to a family of six elements known as Platinum Group Metals or PGM’s (the others being ruthenium, rhodium, osmium and iridium). These metals are so closely related, they are always found together in the natural state. Platinum is 100 times rarer than gold whilst palladium is rarer still.

Like diamonds, platinum and palladium originate within the earth’s mantle. When basic and ultrabasic rocks erode through weathering, these durable, heavy metals are released. Although the extraction process is complicated and the yield low, the process is made commercially acceptable by the high redemption value of these metals; their importance in some scientific applications; their popularity in the manufacture of expensive jewellery and the fact that gold and other rare metals are frequently found amongst the same alluvial deposits.

Palladium was first discovered by the English scientist William Hyde Wollaston, in 1803, who named the silvery-white metal after the asteroid ‘Pallas’ that had been discovered at around the same time (Pallas is the Greek God of wisdom). Although palladium is mentioned in antiquity, and was certainly known, its rarity and extremely high melting point (1552 degrees Celsius) meant that it had never before been isolated in the pure form nor used for any recorded purpose.

The Platinum Group Metals are all noted and revered for their physical and mechanical properties. Palladium, like the other PGM’s, is an extremely stable and inert metal and cannot be attacked by the sulphurous compounds and other atmospheric pollutants that pervade city atmospheres and inevitably tarnish more reactive metals.

The Characteristics of the Platino-Palladium Print

Over the years, photography has employed many different forms of physical expression. From its very beginnings with Fox Talbot’s Salt print (through all the subsequent incarnations such as Albumen prints, Argentotype’s, Cyanotype’s, Kallitype’s and the ubiquitous Silver Bromide emulsion) to contemporary mainstream dye-sublimation and ink-jet types, the Platinum/Palladium print has remained unchallenged in the realms of image integrity and longevity.

These rare, noble metals, used either independently or in combination, produce images of exceptional tonality and richness. The Platino-Palladium print has long been admired for its beguiling nature and for the subtlety and clarity that it conveys. Detail in even the deepest shadows and a delicate, ethereal dimension to the highlights complimented by a rich set of tonal values in between imbues this process with an effortless beauty. It is this enigmatic quality that allows a Platino-Palladium print to transcend the luminosity achievable by all other more mundane, commercial methods of reproduction.

The properties of palladium are perhaps less well known than platinum, but being a sister metal, it has similar physical and chemical properties although the two metals demonstrate quite distinct properties when it comes to the finished print. In Dr Mike Ware’s process, the tone of the final image can depend upon several factors: the relative humidification of the paper prior to exposure and the influence of the physical properties of the paper on the sensitizer to name two; but all things being equal, palladium will yield a warm black to sepia image, whilst platinum will produce a more neutral to blue/black colouration.

Sharpfoto’s prints have been produced using a combination of pure platinum and palladium. The composition is biased heavily towards palladium but this choice owes nothing to cost considerations (palladium is usually cheaper than platinum but between 2000/2001 palladium was twice as expensive as platinum), but exclusively to the warm black colouration and slightly increased range of tonal values that palladium yields. This warm black is better suited to convey the particular qualities and individual style inherent within Sharpfoto photographs. If required, tones between blue/black and sepia can be achieved by mixing the two metals in varying proportions in the sensitizing solution.

It is of course true that a Platino-Palladium print doesn’t turn a bad photograph into a good one, nor will every image possess the visual characteristics necessary to exploit the major advantages of the process; however, it would be very difficult to dispute that a well crafted Platinum and/or Palladium print displays the aesthetic and archival qualities that all others aspire to.

These favourable physical and aesthetic attributes have allowed the Platinum/Palladium print to ascend the visual hierarchy to the extent that they now enjoy an almost mythical status in the theatre of photographic reproduction. This has been helped no doubt by the process being preferred by the (mostly American) greats of the medium. Alfred Stieglitz (who referred to the process as ‘the prince of media’), Edward Weston, Edward S. Curtis and Irving Penn all produced exceptional works in platinum. Perhaps the pre-eminent advocate of the merits of the process can be demonstrated by the fact that the greatest of them all – Frederick Henry Evans – refused to use any other medium. His refined images of British and Continental cathedrals are, in many opinions, the finest of their genre and are unlikely ever to be surpassed. When the supply of platinum dried up, Evans saw no point in continuing. To him, photography (or at least his vision of the medium) could only find its ultimate expression through the Platinotype - they were intrinsically linked. To use lesser metals would be a compromise that a purist like Evans could never contemplate. The futility of using anything other than platinum ultimately bothered Evans so much, he gave up photography altogether.

The Chemistry of the Platino-Palladium Print

In Dr Mike Ware’s process, the sensitising solution is prepared by mixing an equal quantity of ammonium iron (III) oxalate with ammonium tetrachloropalladate (II) and/or ammonium tetrachloroplatinate (II). This solution is then coated onto paper manufactured specifically for the Platino-Palladiotype process by Pearson’s Fine Papers. After drying, the sensitised paper is exposed to ultra violet light through the negative in a contact frame where the initial chemical reactions take place. In very simple terms, the oxalate anion allows the iron (III) to be reduced to iron (II) by exposure to intense short to mid wavelength ultra violet light (320-350nm). The Iron (II) is then in turn responsible for reducing the palladium (II) (or platinum (II)) into its pure metallic state.

The subsequent clearing and fixing of the print is achieved by successive immersions in disodium EDTA (ethylenediaminetetraacetate), hypoclear and finally tetrasodium EDTA which removes the unwanted iron compounds and any residual unexposed palladium/platinum salts. An extended rinse in fresh running water leaves only pure metallic palladium/platinum embedded within the paper matrix.

The Permanence of the Platino-Palladium Print

Perhaps a Palladium/Platinum print’s greatest asset - aside from its obvious visual strengths - is its image stability and permanence.

A traditional colour photograph contains dyes that inevitably fade, sometimes in only a few years. Although the rate of fading is dependant upon several independent factors: the amount of daylight that the print is exposed to, the prevalent atmospheric conditions that it is stored in and indeed, the type of printing paper used (some papers were significantly better than others) etc., image degradation is inexorable.  A conventional black and white photograph on the other hand of course contains no dyes and has an image that is comprised of silver embedded within a gelatinous emulsion. Although these prints are capable of lasting a long time, the image can still begin to deteriorate within decades. A further problem can arise in some climates (or in poor storage conditions) where the emulsion can become the victim of microbial attack which results in mould feeding off the gelatine that holds the silver image, thus destroying the photograph. Fibre based black and white photographic prints are less susceptible to attack from atmospheric pollutants and, providing stringent processing procedures are observed (including the use of a hypo clearing bath) in addition to selenium toning (which coats the silver particles with silver selenide which is less reactive that pure silver) these prints are capable of a lifetime second only to that of gold and platinum / palladium.

Modern incarnations of the photographic reproductive process have of course progressed somewhat from the older colour negative emulsions in terms of image durability. Ink-jet or dye sublimation printers do not rely on a gelatinous coating and therefore will be no more prone to microbial attack than any other paper based media but the stability of the dyes or pigments that comprise the image whilst perhaps in some cases comparable with that of silver, can only approach a fraction of that of platinum and palladium.

Ink-jet prints are generated by Pico litres (10^{¯12 litre}) of ink ejected by the print head nozzles that manifest themselves as dots (on or slightly under the surface of the paper) typically in the 30-micron range. In the case of dye based systems, fading can occur within months and certainly a few years. Pigment based ink-jet prints – such as Epson’s ultra-chrome range – are much improved and have claimed ‘archival quality’ and light fastness of ‘up to 75 years’ – depending on the paper used of course. This sounds impressive, but since there are no recognised International Standards published specifically for photographic image stability, this figure is based on Epson’s own testing criteria. The main difficulty when trying to evaluate image durability is to replicate conditions that a print maybe reasonably expected to encounter during its lifetime via a simulation compressed within a few months or years.  Image degradation could well feature before this time has elapsed.

The Wilhelm research institute publishes extensive test results regarding image permanence in the field of photographic reproduction, and, whilst the results can never be exclusively authoritative, they are the best indication available on the massive improvements made in image durability and the relative merits of one contemporary system over another. It is important not to denigrate ink-jet systems, nor to question the seriousness with which their manufacturers treat archival considerations. Photographs printed on high quality paper with pigment based inks are already a massive improvement on conventional colour negative printing papers to the extent that they surpass the quality achievable of conventional colour negative printing papers.

In a way, the current status of image integrity only serves to demonstrate that the definition of archival is inevitably subjective and dependant upon what is deemed as acceptable image durability, but, to put all other forms of mechanical reproduction into context, a well prepared platinum/palladium photograph can easily last many hundreds if not a thousand years. This permanence is unique in the realms photographic durability and is attributable to the chemical inertness of the platinum/palladium metals and the purity, strength and archival quality of the paper. A Platinum/Palladium print is composed of grains of these pure, precious metals embedded within the cellulose fibres of the base paper: nothing else.

The Enigma that is the Platino-Palladium Print.

All in all, a Platino-Palladium print is at the very least, a highly unusual and rewarding visual experience. The complexity and cost of manufacture is such that the printing process is self-regulating: only the very best or most important negatives will make it to the printing stage. Very often, modern technology makes things easier and more reachable to the masses (which, on the whole, is a good thing), but not always necessarily better. Most of us have been conditioned to accept the quality of digital output as being comparable to, or better than ‘photographic quality’ without questioning the objectivity, validity or relevance of such claims.

It is an accepted axiom that the human eye is ‘only’ capable of resolving detail up to 300 dpi. This is the fundamental law that vindicates ink-jet’s popularity in all aspects of the photographic medium and is not disputed - although it must be stated that ink-jet resolution is not analogous to conventional lithographic halftone dpi. What is questionable though, concerns the reasoning that proposes that a photograph should be reduced to a mathematical equation based on visual acuity alone. The empirical evidence suggests that there is far more to a fine photograph than millions of two pico-litre dots ejected from an ink-jet printer. It may prove impossible to provide quantifiable mathematical data to justify the Platino-Palladium print’s visual authority over all others, but perhaps, therein lies the enigma.