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                                Gum Over Platinum
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Gum Over Platinum

By Clay Harmon

A first timer’s summary with methods developed by Stuart Melvin, Kerik Kouklis and Stan Klimek

The Guts Print

This is the underlying palladium or platinum print over which you are going to put the subsequent gum coats. My philosophy is to make a print with the highlights right on, with the shadowed areas being a little lighter than normal.  This can be achieved by using a lower-than-normal contrast palladium mix and exposing so the highlights are correct, and allowing the shadows to remain somewhat weak. This will give you some 'running room' for putting color into your print. If you are already at your lowest contrast mix, there are ways you can get color into the print without blocking the shadows, but that is the advanced class.

Which brings us to paper. The ideal paper would be a body-sized hot press paper in the 130# or so weight with a nice neutral to acidic pH. Whatman’s Watercolor 130# hot press is my pick for the easiest beginner’s paper. It merely needs a brief dip in 1.5% oxalic acid and it is ready to go. Fabriano Extra White needs a good five minute soaking in oxalic to make it platinum ready. Rives BFK is another good choice, but this paper shrinks significantly, has some texture, and will need at least two hot water soak-and-dry cycles prior to treating with the 1.5% oxalic acid.

Easy Credit - Platinum

Platinum Print

Easy Credit - Gum over Platinum

Gum over Platinum Print

Copyright 2004 by Clay Harmon. Click to enlarge.

For your first print, pick an image that might print just right in palladium with a #3 dichromate blend (4 drops/200ml) and use a #2 blend (2 drops/200ml) with slightly less exposure to keep the highlights from getting too dark and muddy. If you are using Fabriano EW, it will be a print with decent blacks by default. For this paper, just use the same platinum or palladium contrast mix that would normally yield a nice print. Clear, wash, and hang to dry, and then while still damp, realize that...

Size Matters

Size the palladium print with a 4% gelatin sizing. I know, I know, you don't want to size the paper. Tough. You gotta do it to get the control. Here is the drill: Get a pyrex 2 cup glass measuring cup. Put 125ml of distilled water at room temperature in it. Add 5g of gelatin and let it ‘bloom' for 20 minutes or so. Get a larger container (8 cup pyrex measuring cup is what I use) and add some 160 degree water. Place the smaller measuring cup in it, and stir the gelatin occasionally as it dissolves. Keep a thermometer handy, as you don't want it getting much hotter than 140 degrees, but that shouldn't happen as the hot water cools toward ambient. When it is fully dissolved, add about 1 dropper 'shot' of Everclear, and then add about 4-5ml of 40% glyoxal. Use a dedicated hake brush to coat the damp print on one side, working the brush back and forth in both directions to make sure it is completely and evenly covered

This document is intended to get a first time gumover printer on the road to colorful prints. Show any of this to an experienced old-school gum printer and they will tell you that it is nonsense and furthermore, you are pond scum for believing any of this obvious marlarkey. Opinions are numerous and tempers short in the tiny little world of gum, But keep in mind the words of this famous philosopher:

“To me, boxing is like a ballet, except there's no music, no choreography, and the dancers hit each other.”
-Jack Handey.

One note: Do not use the glyoxal sizing if you are not going to get around to doing your first gum coat in the next two days. It will start to yellow if you don't put it through the gum steps. Once you have put it through at least one round of gum, you will be fine. Why? I do not know, except it works. The yellowing is not a problem with formaldehyde or chrome alum hardened gelatin, but I don't use formaldehyde because it is smelly and hard to get, and the chrome alum takes about 3-4 days to harden. Hang the print until it is matte, then lay it on the screen to dry.

Throw Some Color Around

Add 0.4g burnt umber and 0.2g indian yellow to a mortar, and then add 10ml gum. Grind it with the pestle until it is smooth and creamy. Add 10ml of 30% ammonium dichromate, and mix it thoroughly. Finally add 8-10 drops of everclear. Grind until smooth, and then pour it onto your pickup tray and pick up the gum mix with a clean roller. Roll it smoothly onto the masked print using back and forth motions in both directions until it is completely smooth. Gradually reduce the pressure on the roller and the coating will smooth out nicely.

Put it under a cool fan and dry. Make sure it is dry! Dichromate and silver gelatin negatives are not compatible! On a light table, place your negative on top of the print and align it until it is registered. A piece of glass or the negative sleeve can be placed on top of the negative to assist in flattening the negative against the print. Carefully tape one or two edges of the negative to the print with scotch magic soft-release clear tape.

Expose for 80% of your palladium exposure. This will push some color into about zone VI or VII.

Remove the negative and then slide the print into a tray of 70-75 degree water, face up, and give it a couple of shakes under water to remove any air bubbles, then slide it out and place it face down for 30 minutes. A lot of people change out the water 3 times, but I think this is unnecessary. I haven't done this in over a year, and I don't have any problems. The soft unexposed gum and dichromate will gradually fall off and turn the water an interesting orange color.

Examine the print after 30 minutes by picking it up carefully and observing if your highlights have cleared. If they have, you can then rinse the print in cool water for 5-10 minutes or so and dry it by hanging until just damp, then put it on the drying screen. Be wary of putting a sopping wet gum print directly on the screen, as there is usually a small amount of pigment still running around that will end up in a puddle in the middle of your print, ruining it.

I’m Stoked, I Want More


After the paper is dry, use the same procedure, but use 0.5g burnt umber 0.1g green gold, 0.1g perylene maroon, and 8ml of dichromate. Expose for 30% of your base palladium time. All other steps are the same. The lower amount of dichromate and higher pigment concentration, coupled with the lower exposure time will put some darker color just in the shadow areas.

Gum Generalities

  • More dichromate  = more speed, less contrast
  • Less dichromate  = less speed, more contrast
  • More pigment =  less speed, more contrast
  • Less pigment =  more speed, less contrast
  • Yellow /brown/ orange pigment  = slower speed
  • Blue/violet/ =  faster speed

Seat of the pants exposure ‘rules’ (Hah!) for brownish pigments:

  • 20% of platinum exposure- full dichromate load (30% g/ml) - color goes to ~Zone III-IV
  • 30% of platinum exposure- full dichromate load (30%g/ml) - color goes to ~Zone V
  • 40% of platinum exposure- full dichromate load (30%g/ml) - color goes to Zone V-VI
  • 80% of platinum exposure- full dichromate load (30%g/ml) - color goes to Zone VI-VII

If you want to get color all the way into the highlights - (fun now and again if you want a yellow sky or something) back off the pigment to about 1/2 your 'normal', and use a lot of dichromate, and expose for 150% of your platinum exposure. Your mileage will vary. There are a lot of variables here....

Article and images copyright 2004 by Clay Harmon.  All rights reserved.
No part of this article may be reproduced in any form with the express permission of the author.



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