Decals can prove to be one of the aspects of building plastic models that cause the most headaches when it comes to achieving a satisfactory result. Most of the common problems can be solved by following a few simple steps.
Preparing the Surface
Before embarking on adding the decals to your model it is important to have the correct surface for them to adhere to. Decals stick best to a clean, smooth finish so most modellers will apply a gloss varnish or use gloss paints to achieve a smooth surface on which to apply the decals. A final layer of varnish can be added later to change the finish.
You can apply decals onto a matt surface, but the slight rough texture can increase the chance of the a 'silvering' effect under clear sections of the decals, which is caused by tiny air bubbles under the decal. Decal setting solutions can help with this, but we will discuss them more later on.
Placing the Decal
Make sure to leave enough time for the paint or varnish used has fully cured before applying decals. For enamels this can take a few days.
To separate a decal from the backing paper it will need to be soaked in warm water. The hotter the water is the faster it will separate, but be careful not to make the water too hot. In warm water it usually takes around 30 seconds for the decal to lift. Don't be tempted to try and slide the decal off the backing paper until it moves easily, if the decal is forced it is likely to tear.
Once the is free of the backing paper it can be slid into position on the model. I highly recommend holding the paper against the model in the correct position, hold one edge of the decal in place, and slowly move the paper away from underneath so that the decal can settle onto the model. If you try to remove the decal from the backing paper before placing it in position it has a habit of curling up on itself.
When the decal is in position you can gently dab it with some paper towel to remove any excess water.
Do I need a decal setting solution?
A decal setting solution isn't necessary to put decals on your model. However, they will greatly improve the finish, soften the edge of the carrier film visible around the decal so that it blends in better with the surface underneath, and allow the decals to settle into recesses and across uneven surfaces such as into panel lines on an aircraft model.
If you are using any setting solutions, then now is the time to apply them to the surface of the decal. These will result in the decal becoming very fragile as it settles into or over any surface details such as panel lines, or rivets, etc. This is best done at the end of a modelling session so you aren’t tempted to ‘help’ the decal settle in. The decal may crinkle up, but don't worry, it will settle down again as the solution dries. Should the decal need to conform to any compound curves or larger surface lumps and bumps then repeated gentle applications of softening solutions may be required.
Should any ‘silvering’ appear underneath clear sections of the decal’s carrier film the surface can be pricked with a pin and more softening solution used to help them conform to the surface better.
Protect Your Decals
When all the decals have been added to the model, and you are satisfied with the result, they can be sealed in with a second coat of gloss varnish, this helps to blend their appearance in with the rest of the finish as they tend to be fairly shiny.
After the second gloss coat is dry any weathering techniquies can be employed, before these are then sealed with a final coat of varnish that will give you your desired finish.