In recent weeks quite a few people have asked me how I deal with Plague Spots, so I thought a short article on these horrible things could be helpful.

Plague Spots are what I call the nasty, ugly black dots which appear on platinum and palladium prints. The small ones appear as tiny black specks, but the big ones can be several millimetres across.

If you look at a Plague Spot through an 8x linen magnifier you’ll see a dark central dot surrounded by a slightly paler, and much larger, corona. Sometimes the corona will be round, and sometimes it will be comet shaped (the shape depends on how the developer was moving when the Plague Spot developed).

Plague Spots used to drive me mad because many of my prints are high key, and just one of these nasties almost anywhere will ruin the print. (According to one of the quirky laws that govern photography, the largest and ugliest Plague Spot will invariable appear in your most subtle and critical high tone area. I once had to make eleven 14x11 prints before I could get one that was sufficiently clean.)

Thankfully I’ve now developed a way of working which manages the number of these down to an acceptable level. Although the process will not eliminate Plague Spots, it does ensure that the few which do appear are small and generally unobtrusive.

Can Plague Spots be Eliminated?

Unfortunately, I have not managed to entirely eliminate these horrors. I have come to the conclusion that even if total elimination is possible, it is not practicable. Hence my approach is aimed at their reduction rather than elimination.

Initially I was uncomfortable with the notion of accepting the small ones as an artefact of process, but then I discovered that even Irving Penn’s prints suffered from the occasional Plague Spot.

Can Plague Spots be Spotted Out?

Unfortunately the answer to this is also, in my opinion, no. They are in the fibres of the paper so they can’t be scratched out with a blade, and trying to spot them with white paint tends to just make an ugly mark even more ugly.

I have heard about people using strong and very noxious chemicals to remove them but this is not something I’ve tried.

Two Competing Theories about their Origin

There are two theories about the origin of Plague Spots. The first is that they are caused by tiny iron particles embedded in the paper. These particles could be from cotton picking machinery or from paper making equipment.

I believe that this theory is wrong.

While it is certainly the case that paper may have specks of iron trapped in the paper fibres, I believe that these mostly wash out of the paper during the processing. I have never been able to link a speck of metal seen in the paper surface before coating, with a Plague Spot in the finished print. And I’ve often seen large Plague Spots where there was no visible metal contamination.

Having said that, specks of metal are mostly easy to flick out of the paper with the point of a scalpel blade, so there’s no reason not to remove them if you see them.

The second theory is that they are particles of platinum and palladium salts which have formed in the metal solutions, and have then found their way into your paper coating.

I find this theory much more compelling because: (1) it fits what I understand about the process by which an image is formed in the print; and (2) the techniques that I’ve adopted to reduce the number of plague spots are based on the belief that this theory is correct – and they work.

So until I see contradicting evidence, this is the theory that I accept.

My Approach to Reducing Plague Spots

I’ve adopted two main strategies for reducing Plague Spots: (1) try to reduce the amount of particulate matter in the bottles of platinum and palladium solutions; and (2) try to stop that which is present from getting into my paper coating.

The first step is to assume that there is Nasty Stuff floating around in your metal salt solutions. This will tend to sink to the bottom of the bottle when it’s left to its own devices, so clearly it makes sense to minimise agitation of the bottles. I therefore keep my bottles on the work surface where I use them, and I try to make sure that they never move except when I top them up. I also try to keep one or two centimetres of metal salt solution in each bottle so that there’s plenty of room for the Nasty Stuff to sink to the bottom where it won’t be draw up into the pipettes which I use to measure out the coating.

As an extra precaution, I also keep the bottles under a wooden box so that they are protected from stray UV light. (As an aside, a Victorian party trick was to use masks and UV light to form shaped crystals in bottles of platinum salt solutions. I consider crystals of metal salts in the solution to be Nasty Stuff so I want to stop them forming.)

Finally, when I need to top up the bottles from my reserve metal salt solutions, I do the following:

  1. Pour the remaining solution into a glass beaker
  2. Add some more of the applicable solution from my reserves
  3. Heat the topped up solution in order to dissolve anything that will dissolve
  4. Pour it back into the bottle through a paper filter to remove any Nasty Stuff which refuses to dissolve

While the bottle is empty I wash it thoroughly with distilled water. And if possible I leave the solution to stand for at least a day in order to let it settle.

I use two techniques for minimising the amount of Nasty Stuff which gets into the paper coating.

Firstly, I try to minimise the amount of Nasty Stuff which gets sucked out of the bottle by the pipettes I use for measuring my solutions. This is easily accomplished by keeping the end of the pipette close to the surface of the solution and drawing the liquid in slowly (hat tip to Scott Davis / Flying Camera for this). This is sufficient for test prints, but sadly it doesn’t guarantee a clean solution.

When I’m making final prints I go one step further. Once the solution is mixed, I draw it into a small syringe, attach a 0.2 micron disc filter, and then push the solution through the filter. These filters are used by biologists to remove bacteria from water, and it turns out that they’re also pretty good at removing Nasty Stuff from platinum / palladium salt solutions (hat tip to John Mullins for this).

The final, filtered solution is about as clean as it’s practicable to get. Now it’s ready to be used to make beautiful platinum prints.

So that’s how I’ve learned to reduce the number of Plague Spots in my prints. No doubt there are other ways that people have found. Does anyone else have any good tips?