If you want to freshen up old wall tiles by covering them with something new, consider painting them. Tiles don't easily take paint -- it tends to come off the surface. You can fix that tendency, however, by deglossing the surface before you start, then using sealing primer to get the paint to stick. Polyurethane seals it all in. Don't do this on tiled walls in the shower or surrounding the bathtub, as the heavy exposure to moisture may make the paint come off anyway.
Go over the tiles with a power belt sander and rough sandpaper. Don't try to take pff the tile glaze -- you won't be able to -- but dull it with the sandpaper. Sand just the tile surfaces, not the grout in between. Wipe off the dust with a clean rag.
Brush on sealing primer, covering just the tiles, not the grout. Brush it on with smooth, even strokes, all going one direction. Let it dry for eight hours.
Apply your selected paint to the tile surfaces with a paintbrush in a thin, even coat. Don't try to cover the tile all in one coat. Let the paint dry for eight hours.
Brush on a second coat of paint in the same manner. Let it dry for eight hours. Add a third coat, if necessary. Let the final coat set for 24 hours.
Brush on high-gloss polyurethane over the tile surface -- not the grout. Apply the polyurethane in a thin coat, with the brushstrokes all going in the same direction. Brush to avoid creating bubbles in the finish.
Let the polyurethane dry for eight hours. Buff it lightly by hand with fine sandpaper to dull the shine. Wipe off the dust with a clean rag.
Apply three or four coats of polyurethane to the tiles in the same manner. Buff each coat before applying the next one. Don't buff the final coat, but let it set for 24 hours before using the surface.
You can paint all your tiles a solid colour, paint them with different colours in a pattern, or paint designs on them. If painting designs on the tiles, start with two solid-colour base coats and paint the designs last.