Painting is the most common way to decorate a box, but there are also Alternative decoration techniques.
Most of the boxes that can be used for housing effects are made of aluminium, but the following should work on steel (e.g. electrical junction boxes) also.
Practice on at least one box before working on a real project, to get a feel for the techniques involved. With a little experience, and constant attention to detail, there is no reason why you can’t achieve a “professional” looking result every time.
Step 1 - preparation
Make sure you have drilled _all_ the holes you need to for mounting controls. The odds are that if you try and drill holes after painting is complete you will slip and the bit will chip or scratch the paint. Try and make the painting the last thing you do (besides mounting the hardware). Check to make sure that all drill holes edges are filed flat (so there is no “lip” for paint to pool up against). To make the box easier to handle, try screwing it together over a coat hanger or some bent wire - you can use this as a handle when painting, and to hang the box from when it is air-drying.
Step 2 - cleaning
If you are using an aluminium box, then there will be a oxidised layer that needs to be removed prior to painting. This can be done with fine sandpaper, steel wool, or whatever. Once the box is nice and shiny, use methylated spirits to remove all the grease and oil from the surface. White vinegar also seems to work well.
From this point on try and avoid handling the box - use the handle created in Step 1.
Step 3 - priming
Paint the box with primer (etch primer if it is an aluminium box). If you are going to do two coats (recommended), it isn’t so important to get the first coat perfect. Try and keep the coat thin (so it doesn’t run, and dries faster), but also make sure you cover all of the raw metal. Hang the box from the handle until it is touch try (15 minutes - 1 hour, depending on the paint you use), then pop it into a toaster oven, or equivalent, at about 200F for 30 minutes or so. Ensure that no painted surfaces are touching anything inside the oven (you may wish to undo the lid and sit the lid and box separately inside the oven during this step). WARNING - the fumes given off during the baking process are toxic, dangerous to your health and generally stink! Keep well clear, or better still, place the oven outside in the open air. Once time is up, give the box a little while to cool down, and remove it. Repeat with another coat of primer (you can sand between coats, but I never bother) if desired.
Step 4 - painting
Enamel paints seem to work best for effects boxes, and it is possible to get a wide range of colours both as “household use” paints or as “car” paints in auto stores. It is easiest to get these in a spray-pak, and this will give you better control over the amount of paint you lay down. Holding your box by the handle, paint with even strokes about 15 inches away from, and perpendicular to, each surface. Practice making smooth strokes on a bit of paper first, pressing the spray button just after starting each stroke begins and releasing just before each stroke finishes. You want to lay down an even amount of paint on each pass, not too much (otherwise it will run) and not too little (not as bad, but it will take longer to finish). It is better to build up on the paint shade gradually with many light coats than lay down a few really heavy coats. Once you are happy with the coverage (the colour, shading and texture should look even on all sides), again hang up the box until it is touch dry, then bake it in the oven again (30 minutes, 200F, experiment and find what works best). You may want to apply another coat, or two, until you are happy with the result.
At this point you may also do any hand-painting: enamels used for painting model cars, acrylics, magic markers, and even nail polish will work.
Step 5 - finishing
Apply several layers of clear paint for protection. You can bake between coats for additional sturdiness, but test out your clear-kote before baking. Some kinds will turn yellow or crackle if baked too hot or too long. Or perhaps you like the crackle effect?
You may wish to label the box before applying lots of coats of clear. It just depends on the effect you want: the labels can appear directly on the paint, or seem to float above.