When applying makeup on gelatin, you first need to seal it, if it hasn’t already been made as part of a GFA, with the G (for gel) being gelatin. If you apply makeup directly onto the gelatin, the color will be absorbed into the gelatin instead of sitting on top; depending on what you are using to color the appliance, you could also begin to dissolve the gelatin if you aren’t careful. You can use a number of materials as a sealer, including plastic cap material, Kryolan Fixier spray (spray a small amount into a cup along the edge of the cup, then brush it on), WM Creations’ Shiny Sealer or Soft Sealer, Premiere Products’ Green Marble Selr®, BJB SC-115 acrylic sealer, or the like.
Once the gelatin is properly sealed, makeup can be applied normally; RMGP is not recommended. You can use creme foundation color and makeup sponges, but I recommend using one of the alcohol-activated color palettes—Skin Illustrator®, Sta-Color, or Temptu® Pro.
Almost without exception, the appliances you will be putting on will have been pigmented at least basically with a foundation color at the time of casting them in their molds. So your task at this stage will be to finish the job, and that can be done quite nicely by spattering numerous layers of transparent color from one or more palettes, 99 percent IPA, and a few cut-down chip brushes.
The better-made your appliance edges are to begin with and the proper placement at the beginning of application will minimize the amount of correction the makeup will need.