1. Brief description of decals

There are several ways to decorate and advertise products on model railroad structures and rolling stock. These are:-

Brush painting which requires a steady hand and perfect eyesight and a masochistic tendency

Pad painting which is what you see on most commercial models today. To do this at home a lot of time and effort is necessary to complete the “rubber stamp” before applying paint. A consideration if you are painting a large number of similar models.

Dry transfers. These are similar to decals in that they are bought off the shelf to be applied to a particular model but they are applied dry (as the name implies) and rubbed onto the surface. The ink is beneath the surface film and requires a matt finish paint for maximum adhesion.

Decals which are applied wet to the surface by sliding the design off its backing. The ink is on top of the film. Needs a gloss finish for maximum adhesion.

Decals are made by a many manufacturers, both large and small and in fact can be made at home. More on this later. If the exact method of manufacture interests you, may I suggest the April 1996 edition of Model Railroader which describes a visit to the Microscale plant in USA.

There are four main parts to decals – backing paper, gum, film and ink. Obviously the ink needs to be water insoluble. The gum is needed to hold the decal to the backing paper before use and also helps in the adhesion of the decal to the model. See Diagram 1.

  Diagram 1(click on image)

2. Application

In basic terms, to apply a decal to the model’s surface, the decal is dunked in water and when the gum has softened, the decal is slid off its backing paper onto the model. The backing paper acts as a conveyor for the decal to the model. Make sure the gum has completely softened/dissolved before trying to apply the decal otherwise the decal might tear if too much pressure is applied to move it onto the model. If the decal is immersed in water for too long it will float off the backing paper. If this occurs try to capture the decal back on the paper. By that stage the gum will probably dissolve and it may be more difficult to obtain a perfect result.

Two solutions can be used to modify the condition of the decals to aid in the settling of the film over corrugations on the model surface. Micro-set will soften the film slightly and improve its adhesion and is used at the time of initial placement. Micro-sol is applied after the decal has dried and examined for flaws. It will soften the film more than micro-set so that the film will more closely follow the shape of the model surface. Air bubbles trapped beneath the decal can be eliminated by puncturing the decal and reapplying the micro-sol or micro-set.

3. Methodology of the application

For decals to mimic prototype paintwork, they have to give the impression that they are actually painted onto the surface of the model. We have all seen the results of decal application by young children. My handiwork as a child when assembling cars and planes usually meant dunking the decal in water and placing the decal in position according to the model’s instructions, with or without painting the model first and that was the end of the story. When the decal dried, I always wondered why the decal looked so obvious.

  Diagram 2 (click on image)

Now I know why this is so. If the model is painted before decaling (the usual case but some undecorated models are cast in coloured styrene), a gloss finish is necessary for the decals to properly adhere to the surface. Matt finish paints have a microscopic surface that is highly irregular (see Diagram 2). When a sheet of decal film is applied to this surface, tiny bubbles of air are trapped between the film and the paint. This is what makes the decal obvious after it dries. If, however the top paint layer is a gloss, the microscopic surface is very smooth and the decal film can lie on the surface without any air becoming trapped. (See Diagram 3). If a model needs to have a matt finish, a final coat of matt paint can be applied after the decal has set. More on this later.

Diagram 3 (click on image)

Pieces of styrene have decals placed on matt and gloss paint to show the difference.

There are two schools of thought regarding the trimming of decals prior to application. Personally I don’t trim to the edges of the design; rather I trim around the decal film. Most decal manufacturers taper the edges of the decal film so that they are easier to disguise. If the decal is trimmed at the design edge, that edge is thicker and maybe harder to disguise with a layer of paint. Also, any sharp edge on the cutout can snag and curl under itself and an internal corner makes it easier to tear the decal during positioning.
Remember, we are trying to give the impression that the decal is painted onto the surface of the model.

4. Placement of decal

Tools needed – saucer for water, fine tweezers, scalpel blade, fine scissors, tissue, straight edge, small paintbrush or microbrush

Immerse decal in warm, distilled water for < 1 min until decal can move on backing paper. Distilled water is better because there are no minerals and impurities to settle on the painted surface. Warm water will soften the gum faster and the decal will settle better.

Apply drop of micro-set to area. Pieces of styrene show the affect of applying micro-set to improve the adhesion.

Place paper near desired position and slide decal using point of blade or tweezers

Use tissue to blot excess water, moving from centre to edges to remove bubbles. The decal might need to be held in position with the back of a blade or other blunt instrument. Care should be taken as any excess stress on the film can tear it.

If decal moves, reapply micro-set to lift decal, place decal in desired position and blot excess again. Obviously, if the decal is torn, the pieces can be realigned at this stage.

Let dry (overnight?)

If bubbles appear, prick them with blade and apply decal sol/set

For irregular surfaces, apply micro-sol to soften decal. Micro-sol will soften the film more than micro-set. Do not touch the film while the micro-sol is working. The decal will appear to shrivel but eventually the film will settle down over the irregular surface. The application of micro-sol can be repeated as often as necessary to obtain that “painted-on” appearance. It is possible to gain some success to reduce the undesirable matt paint problem mentioned above by perforating the film and applying micro-sol, many times! (Pieces of styrene show the benefits of using micro-sol on rough surfaces.)

5. Finishes

The final step in decaling is to camouflage the edges of the film to attain that painted-on look we have been craving for. The edges of the film will always be obvious under close scrutiny. To reduce this affect, wash the model in warm water and dry overnight then one or two layers of clear paint is applied to the model; gloss or matt depending on personal taste and prototype appearance. Of course a layer of weathering with chalks or paint will further enhance the painted-on look we strive for.

6. Homemade decals

The Alps printer can be used to make commercially unavailable decals and to print white ink. Decals can also be made using a laser or inkjet printer and decal film sheets but it is not possible to print white with these printers. With a little imagination and forethought these printers can be used with white decal sheet.
 

David and I are not sponsored in any way by Microscale. Their products are used in this clinic purely because they are available at all major hobby shops and we know they work.