The Diazo Photo Emulsion method of preparing a stencil for screen printing offers a wide range of possibilities. The technique makes it possible to print fine line drawings, hand and commercial lettering, and photographic half-tone positives. You can choose from the Zoico Coat WRV Diazo Photo or Speedball Diazo Photo Emulsion system. (See Right)
A polyester screen fabric is not recommended as nylon will stretch when used with water-based inks, and as it is necessary to scrub the screen to reclaim it, silk and organdy screens should not be used either.
How to Screen Print using Diazo Photo Emulsion
To start, the screen is thoroughly cleaned to remove any grease (see Mesh Prep Gel) and then coated on both sides with sensitised photo emulsion using a coating trough. It is then placed in absolute darkness and allowed to dry. See the full instructions for Kopimask Zoico Coat WRV (this will open as a PDF).
The stencil is made by placing a “film positive” onto the treated screen, which is then exposed to UV light. A film positive can be made from your design printed onto a transparency, or hand drawn onto draftfilm / polydraw using an opaque ink. The darker the image, the better the contrast and sharper the design. Placing a sheet of glass over the top of the design will ensure better contact with the screen, limit shadows and help to define the edges of the image.
The screen is then placed below a bright light source. Where the light is blocked by the film positive, the emulsion will remain water-soluble. It will wash away after the correct amount of exposure.
The remaining emulsion will have been hardened by the light and act as the stencil (or resist). This is the area of the screen mesh that will prevent the screen printing ink from passing through.
To reclaim the printing frame, ink residue should first be washed off with a soft brush, water and detergent. The exposed emulsion can then be removed from the screen mesh with an emulsion remover.
Please browse the range of products available in the Screen Printing section of the website.