Technical Issues
Towards an Unproblematic Cyanotype Chemistry
The 'Classic' cyanotype process relies unsatisfactorily on an impure chemical, ferric ammonium citrate. My 'New' cyanotype sensitizer of 1995 overcame this problem, but at the price of more demanding chemistry. A third option, the 'Simple' cyanotype, has now (2019) been devised - easy to make up with pure chemicals - and offering a control of contrast not hitherto possible.
Paper for Alternative Printing
Possibly the greatest problem confronting alternative process workers is finding a paper suited to their purposes. Of the numerous commercial high-quality papers on the market, very few 'work' well. This is an account of how criteria were evolved, in collaboration with the skilled hand-papermaker of Ruscombe Mill, which resulted in a sheet that performs superbly with all the iron-based processes.
Chemistry of the Iron-based Processes
This is an attempt to de-mystify the inner workings of these process for non-scientists, by explaining the chemical jargon and equations in accessible language.
An Investigation of Platinum and Palladium Printing
A technical paper on research into the chemistry of these processes, with a quantitative assessment of the differences between them. The importance of controlled humidity in achieving a reliable printing-out method is described. The effects of additives such as mercury(II), lead(II) and gold(III) are also discussed.
Photographic Printing in Colloidal Gold
A technical paper on the novel coordination chemistry that underpins my New Chrysotype process, whereby gold(I) can be stabilised in a ferrioxalate sensitizer. It also offers an explanation of the wide range of colour that is achievable with this process.
The Choice of Cation in Ferric Print-out Processes
For print-out processes, where the image is substantially formed during the exposure, the water content of the sensitized paper is of the utmost importance. This is, in turn, governed by the ambient relative humidity, but also by the chemical nature of the cations present in the sensitizer, for which ammonium is argued to be the best choice.
Papermaking Additives Cause Degradation
In recent years, siderotype prints with some machine-made papers have shown occasional defects, which have come to be called “blotching” because of unwanted “woolly” patches of lighter tone. The possible causes of this inhibition of the printing-out photochemistry are discussed, and attributed to the probable presence of “retention aids” added to the pulp at the wet end of the mill. A plea is made for their exclusion from papers intended for siderotype, in the same way that chalk is excluded.
Outgassing during Siderotype Exposures
All the siderotype processes evolve carbon dioxide gas as a by-product of their primary photochemistry. The quantity of this gas is here calculated, and shown to be a potential source of loss of acutance, i.e. blurring of the printed image, if it becomes trapped between the surfaces of the negative and the sensitized paper. Evidence for this defect is presented, and ways of minimising it are discussed.