Barrier coats. Mold longevity. - 2002 J. Broz    

Silicone molds can hold up only so long after multiple castings.
The curing resins bite into the surface more with each pour. A clear matte finish or
a fast drying primer, or powder coating, can protect the mold surface.
Talcum powder also helps the resin permeate nooks and crannies.

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Spray a light coat of primer.
(One that will accept your final paint choice,)
and assemble your mold for pouring.
Avoid thick, wet coats, as the thinners from the paint can swell your mold surfaces after many coats.

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Occasionally clean your molds out of left over primer build-up. Water, with a light detergent or soap, works well.
Allow your molds to dry before casting again.
Between casts, a good air blasting should lift out primer, or talc residue.