Walnut veneer is very thin, usually no more than 1.5 mm (1/6 inch). It is delicate and needs to be treated with care. It can be hard to tell if the veneer has an oiled finish or an old lacquer finish that has worn off. In either case, you can't use typical cleaning products because of possible damage to the veneer. You must use a product that feeds the wood as it cleans, to enhance and moisturise the veneer.
Pour a small amount of lemon oil onto a soft cloth in the palm of your hand.
Apply the damp cloth to the veneer, smearing the lemon oil around with a circular motion. Begin scrubbing the veneer with the cloth. Scrub parallel to the grain with short strokes moving forward 5 cm (2 inches) and backward 2.5 cm (1 inch) in a continuous line.
Pour more oil into the cloth if it gets dry and continue scrubbing. Use a dry cloth to inspect the area that you just scrubbed. If it looks clean without any smears or dirt, start another area.
Scrub completely over the surface of the veneer until it's wet with oil. Wipe it thoroughly with a dry cloth. Inspect it for smears, or dirt that you might have missed and spot clean those areas again with the oil.
If you accidentally splinter part of the veneer loose, use a walnut coloured stain marker to colour it back in. For holes, use a walnut coloured furniture crayon. Apply more lemon oil once every six months for a rich deep finish. Use cotton cloth for best results.
Lemon oil is non-toxic but use in well ventilated areas to prevent breathing in large quantities.