Recommended processing for exposures made on BB Lith plates.

BB Lith is ideal for lithography, being capable of a high resolution, sharp edges between exposed and unexposed regions of the plate and a very high density in the exposed areas.
For best results we would suggest using a Gelatin Removal method (outlined below) in order to remove the gelatin from the 'clear' areas of the plate leaving only the transparent glass substrate.
An alternative method would be to expose the plate with a contact film mask negative, develop the plate using a high contrast developer (taking care not to allow the unexposed areas to fog), and then fix the plates. It should be noted that using this method the transparent areas of the plate will not be as clear as would be obtained by the gelatin removal method.

Sequence of gelatin removal processing

Exposure to Mask	Exposure plate with film mask positive, about 8.5 mJ/cm 2
First Development	Kodalith developer, 4 mins at 22° C
Wash	Water, 5 min
Bleach	Bleach plate until all black silver is cleared
Re-Exposure and Re-Development	Return plate to developer under strong white light
Wash	Water, 5 min
Fix	Fix bath diluted as recommended, 2 min
Final Wash	Water, 5 min
Final Rinse	Water with wetting agent, 1 minute

EXPOSURE TO ARTWORK MASK
Being a 'direct positive' process, appropriate positive film artwork masks must be prepared.
Expose the BB - Lith with the contact mask to the routine level of exposure (35s at 0.25mW using a 20W Halogen proved acceptable).

FIRST DEVELOPMENT
Develop the exposed plate to as high density as possible without allowing the unexposed areas to fog. We would recommend 4.5 mins development in Kodalith developer at 22° C.

BLEACH
Mix equal quantities of Bleach solutions A and B. Bleach the plate until the black silver is completely cleared, this may take several minutes with strong agitation.

The recipe is as follows:

Solution A
De-ionized Water	1/L
Acetic Acid	150g
Cupric Chloride	10g
Urea	70g
Solution B
De-ionized Water	400ml
30% Hydrogen Peroxide	200ml

RE-EXPOSURE AND RE-DEVELOPMENT
Expose the plate to strong white light in order to expose what remains of the emulsion layer; and return to the plate to the Kodalith developer to develop these exposed areas to the desired density. Since there is no chance of fogging the clear areas of the plate, the plate can be left in the developer with the exposing light left on.