This is actually my second attempt; the first time I didn’t know about using accelerants with RTV.
Mold attempt 1, side 1:
Matrix medium: Dow Poster-tack, no mold release.
Accelerant: Art Advantage acrylic paint, “Mars Black”, 1/2t water (paint was drying, but still had a good supply of glycerine)
Mold Material: 100% silicone “Liquid Nails” RTV adhesive. Ostensible 16h set time.
Set time: 24 hours
Mold size: 1″ x 2.5″
10h: Mold is sweating paint, firm with no noticeable tack.
24h: Demold. Mold half still wet with paint, sweats paint when squeezed. Removed test component, pressed mold to remove water/paint.
Poster-tack does not adhere to silicone, but does stick, badly, to component and lego mold frame.
Cleaned part, inverted mold.
Mold attempt 1, side 2
Matrix: Side 1 mold
Accelerant: Deco Art brand Bright Blue acrylic paint, no water.
Mold material: DAP 100% silicone RTV caulk.
Mold release: cornstarch.
Set time: 16 hours
Mold size: 1″ x 2.5″, 1/2″ thick
Brushed on initial layer, then packed with gloved hand. Using table lamp as further accelerant.
Mold material much smoother to mix; horrible stench. Adheres vigorously to gloves and brush.
Edit: 7h. Mold is hard, almost completely free of scent. Demolded, and this half is looking excellent. Slight adhesion to lego frame, not nearly as bad as the Liquid Nails half. Cornstarch acceptable as a mold release on legos. Liquid Nails half of mold destroyed in demold attempt (it re-softened somehow), but current half is intact.
Cleaned and rebuilt lego mold, cut primary flat and trimmed off undercuts.
Mold Attempt 1, side 3
Matrix: side 2 mold
Mold Release: Remington aerosol machine oil.
Set time: 8 hr tentative.
Size, method, Accelerant and material: identical to previous test.
Should be good. I hope.