I have used this on Academy decals with excellent results. After applying a gloss coat apply a drop of Testor's clear canopy glue where you intend to place the decal. Apply the decal. Using the back side of an razor blade, form the decal to the form of the area where applied. Put one more drop of cement at the uppermost edge of the decal. This way the glue should get under and cover the decal. Allow to dry and coat with Future.

Try puncturing the decal with a pin or a no#11 blade and apply microsol - sometime it takes a few applications.

This is instant and only takes one application.

The title should say "how to prevent silvering".
yes,decals must be applied to glossy stuff, not flat. It's the flat surface under the decal that causes the silver.

Im in the habit of spraying the entire model with gloss enamel before decaling, then spraying matte over the entire model when done.
I like the idea of applying the gloss goo to just the area where the decal will set. Saves a whole step with the airbrush. I have a project already painted and waiting for decals that I am going to try this on tonight.

If the decal has already dried when the silvering becomes apparent, it's sometimes possible to soak it off again with hot water. Then you can use the white glue mix or a puddle of Future to make it stick down again without silvering. What the glue or Future does is to fill the tiny voids under the decal that caused the light reflecting off the model to highlight the underside of the decal film. If there are no voids, there's no silvering.

I've had good luck with the micro-sol

Decals need a glossy surface for best adhesion. Another method is placing the decal over wet Future. This method will kill any remaining silvering.

I have never had Academy decals apply without silvering. I have tried almost every method, including the one you refer to and found thin white glue to be the only one to prevent silvering.