Photo Emulsion Exposure

A popular method of making stencils for screen printing is to use the Diazo Photo Emulsion.  The screen is prepared with the photo emulsion and a negative printed on acetate is placed on the screen before it is exposed to a bright light source (find out more about Diazo Photo Emulsion).

Here is a useful excerpt from Ruth Brown's book Digital Imagery on Fabric, page 74.  Ruth's book explores a number of techniques including cyanotypes, Bubble Jet Set 2000 and photo transfers. 

‘You can use various light sources to expose a photoemulsion screen ranging from Photoflood bulbs to a sunbed. Received wisdom is that you use a 250w BBA photoflood bulb suspended above the surface on which you will have a screen. The guideline is that the distance from the light source should be something like the diagonal of the screen, if you want somewhere to start. If you are preparing a big screen and you have the light source too close the edges may not get enough light and won’t expose correctly.

Speedball give a chart of suggested timings for two different bulbs:

150 Watt Bulb, Clear Incandescent

BBA No. 1 Photoflood (250 Watt)

These timings assume you are using a foil pie plate above your bulb to act as a reflector

The photoflood bulb can get pretty hot – probably won’t be able to use it in a normal lamp fitting. Ask where you bought the photoflood bulb from what they would recommend.’