To have well-looking labels for various knobs and switches and connectors and lights on all sorts of instruments.
First, the labels have to be designed in precise sizes. A HTML with CSS is excellent for this purpose, as the styles can have sizes (for fonts, DIV elements, table cells...) in millimeters. (TODO: more detailed howto.) Even larger tables with precise spacing (e.g. description of 2.54mm-modulus pins on a larger connector, or a chip pinout) can be made with ease.
Once prepared as webpage, this is then printed preferably on a laser printer.
This step is optional, but suggested for higher durability of the labels.
To provide the printout with a degree of resistance to moisture and abrasion, coating of the paper is required. A "Plastik" spray paint, a solution of acrylate polymer in an organic solvent, was chosen for this purpose.
This phase of the operation is somewhat tricky. A few coats of the spray paint have to be deposited on the paper. The coats have to be thin, must not form drops or a layer thick enough to flow. The first layers should be as thin as achievable. The right amount of coating is achieved when the gloss roughly matches the gloss of the box being used, or when the thickness or water-proofness of the layer satisfies other criteria.
The toner is slightly soluble in the solvent and liquid flowing over the softened toner carries it away and smears it; this is especially bad in areas where high contrast is required, namely inside of thin white letters on black background. The uneven layers of flowing paint also form drops on the paper, which are visible from angle as areas of different gloss and look ugly.
Printing at least two, preferably three, columns of identical labels is a good insurance against having to redo the labels; usually at least one set can be made from the others that is usable even when the paint application was not ideal.
Another possibility is using a laminating foil; the laminating pouches are made from two layers of plastic foil with their inner sides coated with hot-melt adhesve. The foil will attach to paper even from only one side. This may be useful for making e.g. keyboards for little pushbuttons, or other surfaces exposed to abrasion and heavy touch.
To apply the labels to the target surface, an adhesive is needed. Numerous methods are possible, including spray-paint pressure sensitive adhesive, regular adhesive applied with a brush, printing on adhesive sheets (expensive), and more. The easiest way is using an off-the-shelf thin double-sided adhesive tape, the kind with thin plastic foil with pressure-sensitive adhesive on both sides.
The tape is cut to pieces of desired size, that match the size of the labels, and the pieces are applied to the unpainted back-side of the label sheet, over the backs of the labels. (No need to waste more tape than needed.)
The labels then are cut from the sheet. Careful use of scissors is called for here; a razor blade and a ruler are optional, more straight methods for cutting.
For labels with black background, the edges have to be treated as their white color would be too visible. A black marker, drawing a line over the edges, does the job well.
The finished labels then can be applied. The silicone liner foil is peeled off, and the label is applied to the desired place like a standard adhesive label; carefully positioned, then pressed firmly against the surface.
Labels and instrument
The results are surprisingly professionally looking, and the amount of effort required is fairly low.
Black, text-free label can be used for e.g. covering holes, straightening badly cut edges, or masking the presence of screw heads.