Thursday 26 May 2011
Quentin Smith guides us through his methods for shading veneers, which require only the most basic of equipment
The traditional method for darkening veneers is to plunge them into heated sand, gently toasting them to the shade required. All you need is an old frying pan with around 2cm depth of sand and a heat source such as a portable stove. The sand itself doesn't need to be anything special, most beach sand is suitable, as is the sand sold by pet shops. Some texts specify'silver' sand, but in my experience this can be very fine and the tiny grains can get into the pores of some veneers. Builder's sand can be a bit too coarse and some is rather mucky unless washed by shaking in a jar with several changes of water and then drying.
Try it and see
The theory is simple; plunge the piece of veneer into the hot sand, wait, and remove. However, as the sand will rarely be at a consistent temperature and will have a temperature gradient through it in any case, a good degree of 'try it and see' is involved. One cardinal rule - you can always put the piece in again to darken it some more, but you can't lighten it.
This method works fine for the edge of veneers, but for darkening an area in the centre of a sheet a different technique is needed. Spoon the hot sand onto the area, wait a few seconds then tip the sand back into the pan. Repeat until the desired shade is achieved. If the piece of veneer is small enough to be turned over easily, shading from both sides can be advantageous.
As much of my work is modest in size the individual pieces are rarely more than a few inches long.
My favourite tool for these is an old 125-watt soldering iron to which I've added a small trough, made from some aluminium 'U' section,
to hold the sand. I was lucky that the iron had a threaded hole though it, so I could bolt on the trough, but epoxy resin would probably do the job. In addition to being smaller and giving off far less stray heat than the open pan, the temperature of the sand in the trough is reasonably constant from use to use. The iron has another advantage in that for fine work I can touch the edge of the veneer directly onto the iron to achieve a thin, dark line. The edge must always be fully perpendicular to the iron so that the shading/scorching is even right through the veneer, otherwise the degree of shading will change when the picture is scraped or sanded. Avoid moving the veneer flat across the iron as this will tend to draw scorch marks on the veneer, a bit like upside-down pyrography. Again any effect achieved is unlikely to survive the finishing process.
Colours before cutting
Of course, all heat shading causes the veneer to lose moisture and it may change shape as a result. This can be very frustrating when you've spent a good while carefully cutting an intricate shape. Placing the shaded piece between layers of slightly moist tissue can assist the rehydration, but carries no guarantee that the original shape will be retained. The ideal, therefore, is to shade the veneer before cutting the final shape. This can be tricky, but involves marking through the shape of the 'window' in the normal way, but then cutting the insert piece about 2mm oversize. This piece can be shaded as required and allowed to rehydrate before being replaced behind the 'window' and cut to its final size.
Hot air stripper
With care, a hot air paint stripper can be used effectively to darken veneers. Rather than try to point the nozzle at the veneer it's easier to fix the gun in position pointing upwards (it will often have a stand that does this) then hold the veneer in the airflow. Keep the veneer moving to avoid uneven scorching as the airflow may have 'hot-spots'. Watch the top of the veneer closely and remove it as soon as the desired shade is approached, because it will be slightly darker underneath. If possible, turn the veneer over occasionally so that the heating, and therefore shading, is even throughout its thickness.
A useful technique can be to shade a few areas of a veneer sheet in advance of cutting. Once the veneer has stabilised it can be cut as normal, using the shaded areas to best effect just as if they were natural variations.