Can I paint enamel over acrylic, or acrylic over enamel?

Model painting mixes three chemistries that are all called paint and behave nothing alike. Once you stop thinking about the labels and start thinking about which solvent is in the wet coat and what it can dissolve, every combination becomes predictable, including the ones nobody has written a rule for.

Safety

Step by step

1. Sort the paints by their solvent, not their brand.Acrylics are carried in water or an alcohol-water mix and thin with water, alcohol or their own thinner. Enamels are oil-based and thin with white spirit. Lacquers use hot solvents such as cellulose thinners or acetone-type blends. That is the whole taxonomy.
2. Understand what cured means.Acrylic is touch dry in minutes and chemically cured in a day or more; enamel is touch dry in hours and cured in several days. Almost every compatibility failure is actually an impatience failure — a solvent applied over a film that had not finished curing.
3. Put enamel over cured acrylic freely.White spirit does not dissolve a cured acrylic film, which is why enamel panel-line washes over acrylic base coats is the standard technique in scale modelling. Give the acrylic a full day first.
4. Treat acrylic over enamel as needing a barrier.A cured enamel surface is slick and non-porous, and acrylic sits on it as a skin rather than keying in. It appears fine and then lifts when masked, handled or scratched. If you must do it, either key the surface with a very fine abrasive or, better, put a clear coat between.
5. Put lacquer on first, not last.Lacquer solvents will soften and lift acrylic and enamel underneath. Lacquer primers and lacquer base coats work brilliantly directly on plastic and give the hardest, thinnest film. Once you are past that layer, do not go back to lacquer.
6. Use a gloss coat as your barrier and your working surface.A gloss clear coat over the base colour does three jobs at once: it isolates the layers below, it lets decals sit down without silvering, and it lets an enamel or oil wash be wiped back off the flat areas with a cotton bud while staying in the recesses.
7. Finish with a matt or satin coat over everything.It unifies the sheen so that the gloss barrier, the decals and the differing sheens of the colours all read as one surface. This final coat is what makes a mixed-chemistry paint job look deliberate.
8. Test on a spare sprue when you are unsure.Two minutes with the actual paints you are about to use settles it definitively, and every kit comes with spare plastic. This is more reliable than any rule, including this one.

Tips

• The order almost every scale modeller uses: lacquer or acrylic primer, acrylic colour, gloss clear, decals, enamel or oil wash, matt clear. It works because each step is compatible with the one before.
• Enamel washes are removed with white spirit on a cotton bud. Over a gloss coat this takes the wash off the flat surfaces and leaves it in the recesses, which is the whole effect.
• Some acrylics thinned with alcohol behave more like lacquer than like water-based acrylic, and will bite into a coat below. If a brand thins with its own alcohol thinner, test it as though it were hot.

Common mistakes

• Applying an enamel wash over bare matt acrylic — Matt paint is porous and the wash stains into it permanently. It cannot be wiped back, so instead of a panel line you get a dirty grey area you have to repaint. A gloss coat first is not a refinement, it is the step that makes the technique work.
• Masking over an acrylic coat applied on top of enamel — The acrylic has no key into the enamel. Tape lifts it in sheets, usually taking the enamel with it, and the repair means stripping back to plastic.
• Judging cure by touch — Both acrylic and enamel are touch dry long before they are solvent resistant. The overwhelming majority of lifting and crazing happens because the coat below had another two days to go.

If it doesn't work

Questions people ask