required materials
Please note some of these chemicals are officially hazardous and should only be handled by people who are properly equipped and prepared. Nothing on this page should be understood as permission or inducement to undertake the activities described, which are for information only.
Also be aware that the quantities and concentrations here are suggestions based on what I have found works well for me.
Highh (sic) Image waterproof paper (amazon.com)
palladium (II) chloride – from advanced photography stores such as Bostick and Sullivan, or sometimes on eBay. Prepare a 0.1% weight for weight solution in water. To dissolve the palladium salt you must add extra chloride such as potassium chloride – of about the same weight, or hydrochloric acid (available as muriatic acid from hardware stores) dropwise, under stirring, until the solution slowly clears to an amber fluid. 50mg of palladium chloride in 50ml of water is the correct proportion and will give enough solution to prepare 100 batches of paper, each of about 10 sheets of size 8″x10″.
Simwool Colloidal Silica Rigidizer (amazon.com) is a medium used for support and coating.
sodium borohydride (CAS 16940-66-2) – reduces the palladium chloride to a dispersion of nanoparticles of metallic palladium. Sodium borohydride is white crystalline powder that releases gaseous hydrogen when wet which can be an explosion hazard in sufficient quantities. Happily the milligram quantities needed for our purposes are unlikely to create a hazard, but the unused chemical must be kept dry in a stoppered bottle.
Sodium sulphide (CAS 1313-82-2) is an alternative to sodium borohydride.
polysorbate 20 (amazon.com) – a non-ionic surfactant added as a coating aid. Make a 10% w/w aqueous stock solution for convenience.
Triton X-100 is an alternative surfactant that is more effective and can be used instead of polysorbate 20.
poly(vinylpyrollidone) – with one R and two L’s – or PVP – is available on amazon.com, and is optional. It stabilizes the nanoparticles. Without it your liquid preparation will be dead within a day. If you add PVP the shelf life of the preparation extends to several days. It doesn’t affect the shelf life of the paper once coated. I suggest making up a small bottle of stock solution of 10% w/w water.
surface plate
To coat the paper evenly you will need something that is flat to engineering standards, such as a granite surface plate (grade B is adequate), big enough for the paper size you want to use. Surface plates can be purchased from tool companies. Trying to use something that merely “looks” flat, like a sheet of glass, is likely to result in uneven coating and unsatisfactory results.
coating bar
The tool to coat the paper is a non-wire coating bar, readily available from AliExpress, such as this one: https://www.aliexpress.com/item/1005008157689362.html
Order a handle at the same time.
I have used 1 micron, 4 micron and 10 micron bars successfully.
cutting mat
To help grip the paper and give a more even coat I find it helpful to use a cutting mat on top of the surface plate – something like this:
https://www.princessauto.com/en/8-x-12-in-self-healing-cutting-mat/product/PA0008926859
instructions
To 10g of vacuum-filtered silica liquid add 0.5g of 0.1% aqueous solution of palladium chloride and 1 drop of 10% PVP.
EITHER: Under stirring, add a tiny quantity of crystals of sodium borohydride.
The solution continues to bubble for some tens of minutes as hydrogen is released but it is not necessary to wait for this to finish.
The amount of sodium borohydride needed is very small – typically 5-10 crystals the size of regular table salt is plenty. Within one minute he solution turns from a very pale yellow to a less pale fawn or tan colour as the palladium chloride becomes metallic palladium particles.
OR: Under stirring ,add 2 drops of 1% Sodium sulphide solution
A tan or whiskey colour develops within a few seconds.
THEN: Add two drops of 10% polysorbate 20 or 10% Triton X-100.
Plate by pipetting 1ml (approximately) of fluid in an even bead across the top of a sheet of waterproof paper which is set on the cutting mat on the surface plate. Draw the bead down the page steadily with the coating bar. Set the paper aside to dry.
Rinse and dry the bar if you take more than a few seconds betwen successive sheets.
notes
Vacuum filtering the silica immediately prior to use is recommended, Prints produced with paper prepared with unfiltered silica can be excessively grainy.
Use distilled water when making aqueous preparations. Using tap water means adding random amounts of carbonate, chloride, iodide and iron to your preparations which may have unintended consequences. Supermarket distilled water is cheap.
A magnetic stir plate is strongly recommended for preparing stock solutions of palladium chloride, polysorbate 20 and PVP, and to keep the silica mixture stirred consistently as the sodium borohydride is added.
When prepared with PVP the liquid used to coat the paper has a shelf life of a few days before it becomes viscous and lumpy as the silica gels. Without PVP the palladium nanoparticles clump together and lose their effectiveness within a few hours. You can recognize this has occurred when the fawn or tan colour of the liquid changes to a grey black, and eventually clears as solid black particles of palladium settle to the bottom of the container.
The drying time of the paper depends on which coating bar is used; when prepared with a 1 micron bar the paper is usually touch dry within 5-10 minutes. One letter-size sheet can be guillotined into 4 pieces each of which will fit comfortably fit a a 4×5 film sheet. The coating is not fragile once dry, and may be handled.
The choice of bar determines the thickness of the coating which changes, among other things, the density of the blackest part of the print.
The silica takes at least 24 hours to ‘set’. Paper that is used for printing too soon after being prepared tends to have darker images and shows more coloured stain after printing than paper which is left to set for longer.