Water slide decals (or slip decals) are water-mounted decals generally printed face up and rely on the dextrose corn sugar residue from the decal paper to bond the decal transfer to a surface. A water-based adhesive layer can be added to the decal to create a stronger bond or may be placed between layers of lacquer create a durable decal transfer. I will be showing the second way to apply them using 'ard cote and some testors chemicals.
Here is the tools of the trade. I use Testors products to apply my decals due to the cost, its cheap! Below is 'ard cote, Gloss lacquer, Dull Cote lacquer, paint thinner, decal Set and a weathering kit. Also, the brush you use for this, will be ruined for ever being used for acrylic based paints.
First step is to apply a layer of 'ard cote to the surface you will be placing the decal. This does three important things.
1) It seals the paint from damage the lacquer can do
2) It creates a smooth surface for which the decal can set without creating air bubbles
3) It makes the edge of the decal invisible when done, which is essential in this process.
The second step is to cut the decal from its sheet and dip into clean water. When this is done the paper will turn a darker blue which tells you it has absorbed enough water. Place the decal on a piece of paper towel. Dip a brush into the decal set, apply it to the damp decal and the surface you will apply the decal too. Slide the decal into place using tweezers and blot the decal with a brush to smooth en it out. The decal set solution dries in about 5 Min's
When the decal dries, apply a cote of 'ard cote. This will seal in the decal and prevent the decal from ever being damaged. But now the shoulder is very glossy! not good at all.
When the 'ard cote hardens, apply a layer of dull cote to the area that is shiny. The dull cote will tone down the finish. If possible, do not make multiple passes. The dull cote can damage areas that have been already painted that are not protected by 'ard cote. After this step, I add a touch of weathering to the decal to make it appear painted or natural. Your done!