Sanding varnish
As varnish is called the result of an originally specially developed process technology in painting , particularly in the 19th century was widespread. The aim of varnishing is to use several layers of varnish to obtain a homogeneous, opaque, smooth, even, glossy, and as hard as possible surface.
Requirements in the 19th century
The goal of a smooth and glossy lacquer layer with high opacity was not achievable with the earlier natural resin lacquers and the technology that corresponded to their consistency or was available at the time.
- These historical paints do not "run smoothly", but rather easily form "noses".
- They catch air bubbles more easily.
- Up until the 20th century , there were no lacquers that were naturally “high-gloss” or “semi-gloss”.
In addition, there was a lack of the appropriate tools and knowledge for the spray technology that is common today .
Only the method of applying with a brush was known and available for processing . However, brushing inevitably leads to structure. If you lower the surface tension of the paint with a suitable solvent , the wettability , i.e. the opacity, also decreases due to the lower proportion of color particles. On the other hand, the paint tends to run smoother, that is, to "pull out" irregularities.
In accordance with the material conditions and technical possibilities, the paint was therefore usually applied very thinly in one operation to avoid air bubbles and noses.
Original procedure
In the case of the varnish process, this technique was deviated from and several operations were carried out, which made the process very labor-intensive and material-intensive. First a thick layer of varnish was applied. These are ground until the surface is homogeneous. It was possible (with the first application) that one “broke through the paint” and the surface became visible or that the paint was sanded off irregularly. Therefore a second layer now had to be applied. For this second coat, the dilution was increased in order to achieve a good bond with the first coat of paint and a smoother surface. This second layer was sanded again. When enough layers were applied in this way, the “finishing” began: The lacquer was sanded with different sandpaper or pastes with increasing fineness until one could no longer see any roughness (800 grit). If you continue sanding, the surface first became matt, then silk-matt and finally (when sanding with chalk as a grinding paste) it was sanded to a high gloss and smooth and polished with the pad to remove color (abrasive) or to apply color with shellac .
Price and appreciation
The complexity of the process also explains the higher price of the corresponding products with “luxury paint”. The higher appreciation of sanded lacquer furniture, in turn, results from the unusual result, especially the mirror finish and the light reflections that it creates, as well as the exclusivity of the corresponding products, which is explained by the price, but also through the durability of the thicker and harder lacquer layer. The disadvantage was that the extremely smooth and reflective surface was susceptible to scratching, which had to be taken into account with particularly careful handling.
Today's imitation process
Nowadays, in the professional sector, paint is almost exclusively applied with a spray gun . Special mediators, synthetic resins and solvents ensure that the lacquer can not only be applied very thickly, but also homogeneously, which is why it is not necessary to apply a large number of thin layers. Sanding is only carried out between the layers to improve adhesion, not for smoothing, as modern paints smooth themselves. The effects "matt, semi-matt, high-gloss" appear when the paint hardens due to the material properties. Sanding with extremely fine sandpaper is no longer necessary.
Due to the high workload, the use of the traditional varnish technique in the mass production of furniture has become obsolete these days and is almost only found in restoration technology. “Sanding varnish” as an attribute of furniture can therefore hardly be used as a quality criterion or a reason for higher prices today, but is used as a pseudo-quality criterion in furniture construction. Modern multi-layer lacquers are often advertised as piano lacquer, which usually only means "multi-layer lacquer, solid color with high coverage". Piano manufacturers point out, however, that to date there has been no lacquer "that flows sufficiently well without appropriate post-treatment so that various grinding and polishing processes are always required".
Web links
- Sanding varnish in: The large art dictionary from PW Hartmann . Beyars, Sersheim 1996, ISBN 3-9500612-0-7 (online source).
- Sam Allen: Surface treatment of wood. Vincentz Network GmbH & Co KG, 2005, ISBN 978-3-878-70586-4 , p. 73 ( limited preview in the Google book search).