99% of the sealing which is done by hobbyists is simply a film sealant. To accomplish this you will paint the insignia, remove the stencil and then seal the painted insignia.
Keep in mind, most sealants are acrylic friendly, provided the acrylic has been given sufficient time to cure properly. Testors Dullcote, one of the most popular choices is a lacquer and is used over acrylic paints all the time.
When I try to explain how water based paints stick to stuff, I sometimes use the analogy of taping up a box. If you put tape just on one side, the tape sticks OK. If you wrap the tapes over the edges it sticks better. If you run the tape all the way around the box and stick it back to itself...the only way to get it off is to use a knife.
Acrylics are a bit like that tape. Although you have some interplay with the long chain polymers between surfaces, it is insignificant unless you are painting wet on wet (and there is almost no interplay with the base for metal, HIPS or polyurethane resins). So, each layer of paint is like sticking a small piece of paint to a box. After you have all your small layers, you apply a sealant over everything in order to keep it from rubbing off, much like those small pieces of tape might come loose from the box if you move it around a bunch.
Now, is you use a laquer sealant over a lacquer or enamel paint, enamels or oils on enamels or oils...than you are actually creating a stonger connection between those paints. The solvent i those paints will slightly dissolve the paint below and when it cures the two layers of paintfilm are fused together. Enamel and oil solvents will also fuse the paint directly to HIPS plastics. Lacquer solvents are very aggressive and can dissolve the HIPS plastic (which is one of the reasons ALCAD requires a primer coat...other than gloss black being what they were formulated for). Although those solvents create that interplay between those paints, they dont have the same effect on acrylics or polyurethanes (polyurethanes for the resin figures and acrylics for the layers of paint).
If you strip acrylic paint using a solvent like mineral spirits, you will find the acrylic turns a bit rubbery, but you dont actually dissolve it. If you strip enamels or oils with mineral spirits, it dissolves and almost goes back to being a paint like liquid (withsome chunks). The same thing happens to a less degree with painting over the paints. Your acrylic will be a bit fragile till everything dries again, but after that...it will be as strong as before (and sealed down if you are using a sealant like Dullcote). With enamels, oils, lacquers...they can be smudged when sealing, but again, provided you are careful and dont apply too much over them, then it will all be good once it cures again, and those the new paint will bond to the old.
Clear as fog, right?
Automatically Appended Next Post:
thegrav wrote:Just to clarify one thing quick. I am a painter, as in I paint on Canvas all the time(aside form my Warhammer habit....). Acrylics take 6 - 8 months to fully dry and cure.
What happens if you don't wait this period of time is the varnish or finishing spray chemically reacts with the paint, often times causing it to become darker. Often times you are better off not using a sealer until the paint has chemically cured and dried.
Now I know model/miniature paints use a different formula, but you are still looking at the "few months" side of things. If yo are using Citadel paints, which are water based, you are really just using a slightly different and thinner mixture of the paints I use when I do a large canvas. If you are using an Oil based paint you can have even longer drying times, unless you force it to cure.
ALL that being said. When I have done stencils (both on canvas and on miniatures) in the past I wait until I have a nice surface seal, normally a day or two. This is the stage where most people think it is "Dry" although experienced painters can still feel the tacky residue of the paint. This is when I apply the stencil, I just make sure to have a touch up at hand and ready just in case.
Acrylics on canvas and acrylics on models/miniatures are not the same (well, the paints are the same, but what the paints do and how they are used is different). Even using the same paints (say golden fluid acrylics) the paint on the miniatures will cure in fractions of the amount of ti e needed to cure on canvas. The biggest reason for this is that cure time is tied to film thickness in an exponential fashion. If your paint film is .01
mm thick, it might take a day to cure. If it is .02
mm thick it might take 4 days to cure. If it is .03
mm thick it might take a week. Canvas painters often paint in thicknesses that can be felt, many many times thicker than what will be used on a miniature. Most paint manufacturers can provide the technical information needed to get a handle on cure times (
GW probably wont, by I have gotten it from Vallejo and Reaper, and I know Golden and Liquitex also provides it).
Sealing miniatures before the paint cures fully can lead to fogging of the clear cote. This is especailly true if you use a lacquer or enamel sealer over a water based paint. Moisture and things like drying retarder are still in the acrylic film and need to migrate out. Laquer and enamels do not allow them to migrate, so those substances can lift the sealant and cause it to "fog" (similiar to what happens if decals are not set properly) or it can cause the paint to flake off. When you seal a canvas before it is cured, even if it is with a non permeable sealer...ther isnt a problem. The back side of the canvas is still permeable and the paints can outgas in that direction.