Before you start

 

Warning — please note that working with historical processes brings you into contact with chemicals which if not handled properly can be dangerous to your health and those of others.

Some basic precautions

• Ensure that dry chemicals are stored away from food or areas where food is prepared, and ensure they are out of the reach of children or curious adults
• When handling dry chemicals use gloves at all times, use of a mask and eye protection (dichromates can irritate the respiratory system) are also recommended
• Mixed solutions should be stored in containers that are clearly labeled and kept out of the reach of others
• Ensure that work areas where chemicals have been mixed or used are thoroughly washed afterwards.

Preparing the work area

You do not need a fully light tight darkroom to work in gum. Your basic requirements are as follows:

• An area with a worktable to coat papers that is protected from direct sunlight and fluorescent lighting is sufficient. Depending on the light source you choose to use you will need to consider a suitable space for this to be located
• Once papers have been coated they need to be dried in the dark. A dark cupboard shielded from direct light is fine
• You will also need a space to lay out your developing trays of water — using the bath is perfectly adequate.

Assembling materials

• Scales to weight chemicals and pigment — an Ohaus style three beam scale or an electronic one that allows you to weight down to 0.1 of a gram is ideal
• A selection of flat wide brushes — often the japanese style hake brushes are suggested, but other artists brushes can also be used. You will need several of different widths, one of about 6 cm wide and one about 15 cm wide. I use several different brushes for each of the main colours I use
• Jars to store the gum/pigment mixture in - plastic or glass pill containers work well
• Bottles to store sensitiser solution - brown glass medical bottles can usually be purchased from your local pharmacy
• Mixing cups for combining pigment/gum and sensitiser — plastic medicine measures are ideal - you want small ones (an 8 X 10 print only needs about 5 ml of the gum/pigment sensitiser combination)
• Glass or plastic stirring rods — I have a whole pack of plastic chopsticks
• bowls for putting the emulsion in
• A Contact printing frame — this can be as simple as two heavy sheets of glass, or as elaborate as a vacuum easel
• Lots of newspaper
• A hair-drier — for surface drying the coating once it has been applied to the paper
• Gloves for handling chemicals — disposable latex gloves are best.

Notes on exposure control

Exposure times will vary depending on your choice of sensitiser, negatives, paper, printing lights and to a certain extend your pigment colour. A useful test to arrive at some base exposures is to use step tablets with each of the pigments you plan to use — you will then need to do further tests with the same pigments and your negatives.

As a guide my printing exposures vary from 6-15 mins under a 400w metal halide light.

• Prepare your paper (pre-shrinking and sizing) and select your negatives. Mix sensitiser, either ammonium or potassium dichromate or both
• Prepare gum/pigment mix (I usually mix 10-12ml of gum with my required pigment concentration and combine as required with the sensitiser)
• Before starting to coat your paper cover the work area with newspaper. At the conclusion of your work session ensure that you clean up thoroughly
• lay out your negatives and paper. Use pencil to mark out the borders of the negative to indicate the coating area. If you want to avoid brush marks around the edges of your print, use painters tape to outline the negative area
• Combine the sensitiser and the gum/pigment mixture in a 1:1 ratio (i.e. 2.5 ml of sensitiser and 2.5 ml of gum/pigment) in a plastic measure cup. Stir with a glass or plastic stirrer
• Pour the combined solution into a saucer or bowl
• Dip the brush in the solution, squeeze out excess
• Start brushing the paper lengthways in long parallel strokes, then vertically. Work quickly and try to keep the coating as even as possible. You will feel the coating thicken as you brush it, once it feels heavy stop brushing. The coating procedure should take no longer than 45 secs. Many gum printers also use a dry brush at the end of the coating procedure to smooth the coating
• Now turn on the hair-drier and quickly surface dry the coating before transferring to a dark place to dry. Allow 30-45 minutes for the emulsion to dry
• Once the paper is dry it should be exposed as quickly as possible
• If you plan to do multiple printings you will need to devise a system of registration between prints. I use mapping pins to punch holes through the corners of the negative, which are then punched through the paper. On subsequent printings the pins are inserted into the negative and lined up with the holes in the paper. To assist in positioning I also outline the 4 corners of the negative with pencil
• Tape the negative to your paper and put the paper and negative sandwich in your contact printing frame (I use two sheets of heavy glass) and expose under your UV light source.
• When you have printed your last coat allow the print to dry and then clear any yellow dichromate stain with a 1% solution of sodium metabisulfite or potassium metabisulphite. The print should be immersed in the clearing bath for 1-2 minutes and then washed for 10-20 minutes.