How do I get decals to "disappear"?

First paint the surface with a high gloss. After it dries apply the decals. Pat them dry once you put them in the right spot. Let dry at least 24 hours. Then cover the area with a flat coat. No decal film.
{Dick D}

Here's how I did it when I was supplementing my income by making and painting model RR equipment.

Surface must start out as high gloss, so that reflectivity of surface equals the reflectivity of decal and the surface finish is as smooth as it can be.
Use a large bowl of distilled water to avoid hard water stains.
Soak decal completely off the paper. Using tweezers, grab decal and wash it back and forth carefully so that all trace of decal adhesive is gone. Lift out carefully and lay on a piece of blotting paper. With a corner of a paper towel, sop up any water laying on top of it.
Paint the spot the decal is to lie on with decal solvent, such as Solvaset.
Holding your breath ( :-) ) lift the almost dry decal and place it carefully on the solvent. Use your good, small brush to move the decal gently into position and to "tamp" out any bubbles. If the decal "bridges" a seam (such as a plank groove), don't despair, just let it dry.
(optional) If there is a "bridge", after the decal has dried, carefully cut it with a fresh scalpel blade (Xacto is too dull and will tear it). If there is a persistent bubble, "x" it with the blade. Then paint the decal again with solvent. You can do this several times on difficult, irregular surfaces.
Let dry and harden at least overnight and then spray with "deglossifier" -- I used to use Testor's Dullcoat, dunno if it's still made.

As with any modelling technique, practice on scraps before attempting on your pride and joy. With a little practice, and good thin decals like the old Champion RR line, you can get it so that the film just about disappears from view.
{Earl Boebert}

I am a 20 year old college student who has been building ships for about 10 or so years. My great uncle and I are the model shipwrights of the family and frequently share our occasional epiphanies. One method of making those dang water slip decals actually stick to a model, I happened upon when I grabbed the wrong brush out of the wrong fluid (This glue like stuff instead of water). There is a product out there (don't have the bottle in from of me right now) that I believe is made by Modelmaster. This stuff is meant to be used to make tiny windows for airplanes or for gluing in windows without getting fogging or a opaque look to the run over. This mystery stuff comes in one of those diamond shaped bottles with the long tip on it. The maker also makes a glue with a syringe tip in the same type of bottle. Anyway, all you do is squeeze a bit of this slop out into a mixing dish (only a bit) and add 2 drops of water from your wet brush. Stir it up really well now. After your decals have soaked, go ahead and put them on the model and let them dry a couple of years (no matter how long they dry I can never get them to stick). After they are good and dry, take a tiny detail brush and just apply a bit of it to the surface of the decal, just barely to applying the decal to a semispherical object in which the decal always has edges the stick up and look awful. My theory is that there is some sort of melting that goes on when the glue is applied and the overall surface tension of the glue actually pulls the decal to the surface. The glue will dry with a clear finish, not overly glossy either. If done properly you can not tell that the stuff was actually applied. I have done this on ever decal I have ever used for the past year or so now and it has worked wonders. It is also great to simulate water in buckets on the deck of a ship. Structurally this stuff is pretty rigid too. The nearest description of how this stuff works on the decals is that it laminates them to whatever surface. I hope that my little tidbit of info may be of some use.
{Aaron J Warren}

Sounds like he's describing something like Microscale Krystal Klear.

I don't know if Krystal Klear will melt the decal but plastic model cement would and it's in the RMS FAQ as one of the techniques for old decals which does not stick but I supposed Microsol would be a better solution :-)

While we're on the subject of decals, check out this site for the latest ink-jet decal paper.
{Lim Chan Hiok}