Where the light and heat go through the clear portions of the film to the screen beneath, the thermal emulsion on the screen is hardened. Where the film is black, the heat and light do not pass through the film and so the emulsion remains unchanged.
The screen is then transferred to a spray booth where it is sprayed with a fine water jet. The water washes away the emulsion which has not hardened leaving a screen where ink can pass through the mesh only in certain areas where that colour is required according to the design.
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