Friday, 6 July 2012

Screen Printing with Diazo Photo Emulsion

Selectasine & Speedball Diazo Photo Emulsion
Diazo Photo Emulsion
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 Selectasine or Speedball Diazo Photo Emulsion system.

A polyester screen fabric is 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.

To start, the screen is thoroughly cleaned to remove any grease (see Mesh Prep Gel) and the coated with sensitised photo emulsion with a squeegee.  It is then placed in a dark room and allowed to dry. 

Use a high contrast image
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 plumtree opaque, 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 and help to define the edges of the image.

The screen is then placed below a bright light source and where the light is blocked by the film positive, the emulsion will remain water-soluble and will wash away after the correct amount of exposure (see Photo Emulsion Exposure Fact File page for further information). The remaining emulsion will have been hardened by the light and act as the stencil (or resist). 

You can find out more about Screen Printing techniques from the George Weil Fact File or browse the range of products in the Screen Printing section of the website.

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