Build plate adhesion issues?

[cliffyk]

Photo polymers and the the photo-sensitive "initiators" (the component that starts the curing when exposed to the near-UV light) are typically clear. Opaque (colored) resins are made so by mixing color pigment(s) with clear resin.

Things that are clear are so because they transmit light, things opaque do not transmit light, but rather reflect it--therefore the pigment in color resin blocks some of the curing light preventing it from reaching and "firing off" the photo-initiators.

Less light reaching the initiators = slower curing = longer exposure required.