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
● 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)
● 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
● 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
● 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
● 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
Tom enameling his Sterling Silver Egg.
He has made this to support a gorgeous Chased Gold and Blue Lapis with Diamond Bracelet.
I asked Tom how he planned to enamel this sterling silver egg. He plans to paint Klyre Fire on and sift the enamels. I asked are you planning to counter enamel it? And he said he did not want to. But he knew he wanted opaque enamels.
Here you can see the egg open, and a bit more of the bracelet. Tom has some leaded enamels with several shades of blue. He is going for a look, close to that of the lapis. I mentioned he would need to deplete the surface. This means to raise the fine silver by heating to a red glow and quenching it in acid or pickle bath. He is removing the copper from the surface so the enamel will adhere to it. I have read it can take 4 times. I use 18k gold in my work and when I want to remove the copper in the surface layer before I begin enameling, I have had best results heating and quenching 7 – 10 times.
Tom has enameled and started sanding to get his final finish on the enamel, using sanding pads and in his last application he plans to use cerium oxide. In this case it is not necessary to counter enamel this piece because it is domed and he is only apply a thin coat of enamel. Remember thick metal = thin enamel. He did not have to use flux because his choice of blue will not burn against the silver. But he is unhappy with the uneven surface of the enamels, and believes he had some soft and some hard firing in the group.
After several attempts to sand and re – fire the enamels still are not smooth. An option at this point could be to apply a top coat such as Ninomiya N4. that is a soft firing enamel.
With his multiple firing bubbles started forming. The depleted surface on the sterling silver was not sufficient, for this many firings. He was heating at 1450 for up to 5 minutes. One thing I have found to avoid some of the bubbles would be to raise the temperature thus shortening the firing time. The enamels on the surface will melt faster and give the underneath metal less time to heat. At this point he has to clean or break any bubbles that might hit the surface on this last firing of a soft enamel. A soft enamel means it will flow at a faster rate than a medium enamel thus not firing long enough for the bubbles to resurface.
And a beautiful Enamel Jewel!