The Gum Bichromate Process for Enamels on Steel

Demo by Brenda Radford,  The Gum Bichromate Process for Enamels

This process is an old photographic printing technique, and I learned it from Gretchen Goss in a workshop she gave in Oakland, California in 2009.  She adapted it from photography colleagues at the Cleveland Institute of Art.

I have always been interested in creating images in enamel and this process, though it can be labour intensive, captured my imagination and so I have continued my learning and experimentation in my own studio.  I have created a line of jewelery based on the famous swans we have here in Stratford (some of them come down our stream to visit my studio) and on theatre related images.

Recommended reading on the subject:

Photographers Formulary – instructions for Gum Bichromate – gum printing www.photoformulary.com

Webb, Randall & Reed, Martin  Alternative Photographic Processes:  A Working Guide for Image Makers

James, Christopher The Book of Alternative Photographic Processes Clifton Park, New York

Livick, Stephen  Gum Printing Toronto: Stephen Livick 2001

FACILITY

●      a well ventilated space

●      a source of water, preferably warm

●      a kiln

●      a spray booth for applying emulsion (see photo)

●      compressed air and gravity fed dual action airbrush

●      enclosed exposure booth with a UV light source or photo bulbs 12-18” above surface (see photo)

MATERIALS

●      B/W negative laser printed transparencies

●      photoshop or other photo editing software

●      greyscale images in the size of the finished artwork

●      ceramic oxides – black and dark colours

●      gum arabic

●      potassium dichromate (label it poison)

●      ml measure with tube

●      teaspoon measure

●      porcelain coated steel 24 ga cut to size

●      prepared copper (counter enamelled, white or light colour foundation stoned down)

●      plate of glass that is not UV protected

●      photography developing trays

●      gram scale

●      glass beaker 250 ml

●      liquid thermometer with clip

●      glass stirring rod

●      small crock pot or hot plate

●      plastic funnel

●      clean hydrogen peroxide bottle or other darkened plastic bottle

●      plastic film container

●      panty hose

●      minute/second digital timer

●      gloves and mask

PROCESS

PREPARING IMAGES

●      use your own negatives as long as they are the same size as your finished artwork

●      for all other images:  using photoshop or other photo editing program, convert to greyscale, increase the contrast, resize to the size of your finished piece and finally, invert the image so it is a negative.

●      print your image negatives on a laser printer as a transparency

●      cut each image out, leaving some space around the image for handling

MIXING CHEMICALS

●      potassium dichromate is purchased in crystalline form – you have to mix it with water, as follows:

●      heat 200ml distilled water in a glass beaker to 120 degrees F on hot plate or in crock pot.  Use a thermometer clipped to the side of the beaker

●      add 40 grams of potassium dichromate and stir with a glass rod until dissolved

●      using a funnel, pour the solution into a clearly marked darkened plastic bottle.  It will store for some time.

PREPARING METAL SURFACE

●      make sure surface is clean of all grease and oil using whatever you normally use: pumice, windex, heat cleaning, etc but make sure it is CLEAN

●      if you want to create more than one piece at once, without touching the surface of the clean metal, use masking tape to attach all of them to a piece of cardboard

●      move prepared metal to spray booth.  Stand vertically against back wall

MIXING LIGHT SENSITIVE EMULSION

●      into an old film container or other container that closes tightly, mix 30 grains (a scant teaspoon) of oxide, 6 ml of potassium dichromate (solution) and 6 ml gum arabic.  Shake vigourously to mix and remove all lumps.  You can sieve through panty hose to ensure no lumps

●      pour emulsion into bowl of airbrush

SPRAYING EMULSION

●      set airbrush regulator at 35-50 psi

●      keep airbrush 12” away from the surface while spraying

●      apply in very thin coats, starting the spray off the edge of the enamel surface, turning the metal or cardboard 1/4 turn after each coating for an even and consistent application

●      move cardboard with sprayed enamels to the light booth.  (Emulsion is viable up to 20 minutes)

●      do not touch sprayed surface

EXPOSING THE IMAGE

●      once the sprayed pieces are on the floor of the exposure booth, place the transparency negatives on the surface of the emulsion (dull side down for a film negative)

●      you can place a piece of non UV coated glass over the negatives to hold them tight to the surface

●      turn the light(s) on and time for 15 minutes

DEVELOPING THE IMAGE

●      develop in warm water, upside down, agitating slightly

●      experimentation at this stage results in many variations

●      while wet the oxide is extremely fragile so touching it to anything will wipe it right off

●      let dry with enamel propped vertically

●      once dry, the surface is more durable and can be drawn or painted on, or rubbed off to create brighter whites

FIRING THE ENAMEL

●      fire at 1450 F for about a minute

●      repeated firings can eliminate the image

●      varied temperature and time will create different results

Thank you Brenda for sharing this! Visit Brenda at  www.radfordstudio.com

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