21/01/2018: Today I recovered this blog post from an old database. Please note that I have not edited it, so it reflects my understanding of this topic in 2012. It does not fully reflect my current printing practice. The essential principles are correct though, except for the comment about gold. See my book The Platinum Printing Workshop for information about how to use gold with platinum prints.
“There is a serious difference in the behaviour of platinum and palladium as a coating medium – literature to the contrary is misleading.”~ Irving Penn
Most contemporary ‘platinum prints’ are actually palladium prints, or at best prints made with a mixture of platinum and palladium. There seem to be few ‘pure’ platinum prints made – mostly because of cost but also, I suspect, because they are difficult to make. This is a shame because pure platinum prints are extremely beautiful.
I have wanted to perfect my pure platinum printing process for a few years, and recently I think I have finally achieved this. Here are some of the things I have discovered about pure platinum printing.
In my experiments to date I have used:
- Bostick and Sullivan chemistry (Ferric Oxalate Solution #1, Potassium Chloroplatinite and Sodium Chloropalladite)
- Potassium Oxalate developer (from Silverprint), with as little restrainer (Potassium Dichromate) as possible
- Buxton paper from Ruscombe Mill
I have found that other papers (for example Fabriano Artistico) can hold a good platinum image if properly prepared, but I have concentrated on Buxton because it is by far my favourite paper. The tests that I have done with other papers support what I say below, but the timings and other specifics differ.
Platinum is much more sensitive to developer temperature than palladium. For example:
- With a developer at room temperature (which for me is typically about 22°C), platinum takes perhaps 45 seconds for the full image to appear. (Penn is on record as saying 3 minutes but this could well be due to different papers or chemistry – or it could be that I am stopping too early.) Palladium on the other hand has nearly instantaneous development at room temperature.
- In hot developer (e.g. 65°C), the platinum image develops almost instantly.
- With a room temperature developer, platinum has a much shorter scale than when the developer is hot – in the order of one to one-and-a-half stops. I have not seen this difference with palladium (although I have not really looked for it)
- I have not seen a significant warming of the platinum tones when using hot developer (although again, I have not really looked for this).
- I have not yet properly investigated how developer temperature effects Dmax.
Conclusion: developer temperature has the potential to be an excellent method for contrast control, especially when coupled with a suitable restrainer.
As noted above, the proper development time is dependent upon the temperature of the developer. Shorter development times result in a gritty image, presumably caused by particles of undeveloped platinum which have been washed of the print.
Once fully developed the platinum image is beautifully delicate and smooth.
Conclusion: it is essential to fully develop your platinum print. Currently I develop mine for one minute with constant agitation of the tray.
The maximum density (Dmax) of a pure platinum print is almost totally dependent upon the moisture content of the sensitiser coating. Moisture also has a significant effect on the print’s contrast scale. In order to achieve consistent prints it is therefore essential to have a consistent drying process.
The drying process has three phases:
One. Air drying (ideally in the dark). The purpose of this phase is to ensure that the sensitiser adheres to the paper. Buxton achieves this in under two minutes but Fabriano Artistico takes quite a lot longer.
I air dry coated paper until its surface has gone matt. Normally this takes two to five minutes. The variation depends a little bit on room temperature and ambient humidity, and a lot on how much water my brush adds to the coating.
If you see smudging from the dark areas into the light areas of your finished print, then you have not air dried the paper for sufficient time and the platinum image has been partially washed away during wet processing.
Two. Heat drying (again, ideally in the dark). This phase has two purposes – to stop the sensitiser being absorbed too far into the surface of the paper (which is said to produce dull, lifeless prints), and also to make the paper safe for your negative. If the sensitiser is too damp then it will stick to your negative and irreversibly damage it. That is fine for digital negatives (because you can simply print another one) but it is a disaster for unique film negatives.
Unfortunately, heat drying also dries out the sensitiser which reduces Dmax and reduces the print’s contrast scale. So if you want to achieve maximum Dmax and the longest scale then you need this phase to be as short as possible.
I use a hairdryer for this phase of drying. I used to dry the coated paper for three minutes, but have now shortened this to one minute. I keep this consistent for all print sizes.
Beware: different hairdryers have different temperature and air speeds so you should not assume that my timings are the right ones for you.
Three. Drying during exposure. Most exposure units produce a lot of heat which will dry out your sensitiser during long exposures (reducing Dmax). Drying is accelerated if you are using a split back printing frame with a felt backing. To an extent you can reduce this by placing a sheet of mylar behind your paper, but the best solution is to find a way to reduce your exposure time (more light) and eliminate heat (e.g. fans).
Note 1: I used to humidify paper after drying it, but I have found that this is not necessary if the heat drying phase is sufficiently short.
Note 2: The more moisture in your sensitiser, the more even must be your brush strokes because uneven coating is more visible with a moist sensitiser.
Additives and Toners:
Except when consciously seeking to make palladium prints, I feel that it is better to consider Palladium as an additive to platinum rather than a substitute. A tiny amount of palladium is sufficient to warm the print and will also boost Dmax; too much turns the print brown. Sometimes as much as 50% palladium can be useful. The amount needed depends entirely upon the warmth you want in your print.
Gold Chloride is often cited as an additive (to be included in the sensitiser) and as a toner (to be applied after printing). So far I have only explored it as an additive. Gold Chloride as an additive works with palladium (it creates a slightly odd pink tone in the highlights) but it doesn’t work with platinum. When Gold Chloride is added to Potassium Chloroplatinite, platinum is immediately thrown down in the mixing glass (i.e. fine black particles appear in the glass so they don’t get to reach the print). This is a complete waste of platinum. It is possible that there is something wrong with my method, but for now I have discounted Gold Chloride as an additive. I will explore its use as a toner at a later date.
There are other additives and toners described in the historical sources, but many of these involve fantastically unfriendly metals such as mercury, lead and uranium. I will leave it to others to explore these.
I hope you found these notes interesting and useful. Pure platinum prints are delicate and beautiful – and well worth the effort it takes to make them. Why not try making some yourself?