Half oil
Medium oil or priming oil is a mixture of equal parts of boiled linseed oil and turpentine oil is, possibly diluted with ethanol . It is used as a primer for wood, cork , natural stone, terracotta and neutral plasters or to freshen up old wooden surfaces. Compared to pure linseed oil varnish, half oil penetrates deeper, but does not reach the depth of linseed oil .
In the traditional carpentry trade, it is customary to coat every wood product with semi-oil before leaving the workshop. For this purpose, brushes from the bark of the linden tree were used in the past, which were worked with a hammer after soaking until a brush formed at the end. The treatment with half-oil takes place in principle after all processing steps because the adhesiveness of the wood is greatly reduced after the half-oil treatment. Up to the point of oil treatment, almost all wooden surfaces are very sensitive to dirt, the semi-oil fixes the surface well against dirt up to a depth of a few millimeters and forms a basis for any paint coatings. Without half-oil, wood is only conditionally suitable for painting, as its absorbency is very strong and only a few colors are designed for it. Tools, utensils and other surfaces that are not subject to frequent use are often treated with only half oil. However, this treatment does not constitute preventive still fighting wood protection against pests. The pickling of wood is usually before treatment with half the oil. Half-oil usually emphasizes the structure of wooden surfaces, it also usually becomes a little darker.
It is common that mixtures of oils that are suitable for use on surfaces are also referred to as “semi-oils” if the oil mixture and dilution contain the same proportion. So turpentine oil is now mostly replaced by white spirit ( white spirit ).
Semi-oils are flammable and tend to self-ignite through oxidation and polymerisation . Soaked textiles ("cleaning rags") and shavings (wood) must be stored / disposed of in such a way that fires are avoided.
