Tag Archives: AgCl

Reliable, Total and Economical Coating and Sensitisation of Wet Collodion Glass Plates

Variously described as “historical”, “ethereal”, “otherworldly”, “alchemical”, the particular aesthetic of the wet plate continues to find use by contemporary photographers such as Sally Mann and Ben Cauchi.

The method of coating an even film of collodion on glass plates is quite an acquired skill, and by all accounts an art-form in itself: far from an exact science. Due to the necessity of keeping the plate wet to maintain sensitivity, the process was never industrialised, and each photographer produced and processed his own plates. Recently I have been meditating on the possibility of a more efficient, reliable, reproducible method of coating, sensitizing, and processing wet plates, requiring no particular skill and minimal wastage.

The method I eventually hit upon is derived from, of all things, the electronics industry. (consequently, I doubt that I would be able to patent, or otherwise claim the process) Mass-produced integrated circuits are manufactured upon silicon wafers, using a photography-related processes, called photolithography (which actually more closely resembles etching). This process necessitates the even and repeatable coating of the wafers with a photo-resist. The industrial method for accomplishing this is one called spin-coating, where the circular wafer is held level, and rotated (about the vertical axis) at a constant speed, while the liquefied emulsion is applied at the centre. So long as the rotation speed and the viscosity of the emulsion are controlled, the results are reliably consistent. The exact thickness of the emulsion is controllable, and a precise amount of emulsion maybe used.

It should be obvious how this spin-coating method might be applied to the coating, sensitisation, and processing of wet plates, to increase precision, reliability and efficiency. The apparatus need not be particularly sophisticated: reliable, repeatable results could be obtained with the re-purposed turntable, and a burette or pipettes.

But pause a moment, and consider: The traditional (hand-coated) wet-plate process itself has a particularly physical and performative quality, which lends the images an imperfect “contingency”(as Benjamin might say), and a hand-crafted kind of cachet. This leads me to wonder – having devised a method that removes much of the chance and skill from the wet-plate process – if it’s utilisation might destroy the very qualities of the process that make it interesting and desirable. Would a cleaner, more consistent, more efficient method render results that are too, in a word, industrial?


1 Comment

Filed under Alternative processes, Black & White, Chemistry, Emulsions, Techniques

Heavily caffeinated.

To anyone who knows my ongoing love affair with 1,3,7-trimethylxanthene, you may as well skip over this entry. Those cunning Costa-Ricans (specifically Saul Bolaños) have discovered a silver negative process that utilises coffee in the development process.

The obvious hook is that you have to use their proprietary “photo transfer paper”, which sounds an awful lot like a commercial process dressed in ratty hipster jeans. At least they are kind enough to inform us that it is a “silver-based” process and tell us that the magical compound in the coffee is “CAFFEIC ACID, ( 3,4-Dihydrocinnamic Acid )”.


Also on this page, is a section on making your own silver (chloride) – gelatine emulsion (again using proprietary components), and a method for coating 35-mm glass plates for use in consumer film cameras.

I Just Wish The Web Developer Would Stop Capitalising Every Damn Thing!

1 Comment

Filed under Alternative processes, Chemistry