Linseed oil varnish
The linseed oil varnish is a paint made from linseed oil , a drying agent and other additives. After hardening, it forms a clear, water-repellent protective layer made of linoxin . This is called varnish or linseed oil varnish ; the term comes from the French 'vernis', which means 'lacquer'. The coating is mainly used for wood indoors and outdoors, but also for other materials. In oil painting , oil paints are often made from pigmented linseed oil and various additives that lead to the formation of a layer of varnish on the canvas. Linseed oil varnish is honey yellow and slightly thick.
Pure linseed oil can also form a linseed oil varnish, but is used less often because of the long drying time.
Definition
Neither the craft nor the artistic use of linseed oil varnish has a uniform definition of its composition. However, it can be said that it is a modified linseed oil, the drying properties of which have been improved "through various treatments". In Georg Zerr's handbook of paint production from 1922, varnishes are referred to as “drying oils, which are made into a viscous, somewhat oxidized and polymerized state by heating to a minimum of 150 and a maximum of 320 ° C, often with the addition of resins or metallic compounds in which they not only dry faster and better, but also form a more effective coating for the color materials and a more easily spreadable color. ”Today, linseed oil varnish is often offered with the addition“ double boiled ”and“ resin-free ”. These product properties are approved by the German Institute for Standardization e. V. marked with the industrial standard DIN EN ISO 150: 2007-05 (up to 2006: DIN 55932). In the specialist literature before the end of the Second World War it is said about this term: “The term 'double boiled linseed oil varnish' is nonsense. No varnish is 'cooked' twice. ”The frequently used designation“ resin-free ”also means for the general characterization of linseed oil varnish that resins are sometimes used in their manufacture.
Composition and manufacture
Linseed oil varnish consists essentially of boiled linseed oil. This can also be used without additives to obtain a varnish. The curing process, wrongly referred to as drying, takes significantly longer without additives. Desiccants - so-called siccatives - are heavy metal salts of organic acids that act as catalysts on the hardening process. By boiling the linseed oil veneer, hardening takes place, so that faster hardening and better processing is possible. The disadvantage is the poorer penetration (" knocking away ") into the material to be sealed. Diluting with solvents such as turpentine or orange oil to form a so-called half oil (1: 1 mixture) can remedy this disadvantage of linseed oil varnish. These additives in the half-oil do not lead to the solidification of the linseed oil veneer through drying, but rather serve as a "distribution agent" and evaporate completely. The solidification of the linseed oil veneer to form linoxin takes place through oxidation and polymerization .
Curing
Linseed oil does not dry in the conventional sense through the evaporation of components, but hardens through oxidation , the absorption of oxygen from the air: Oxygen atoms "break" two double bonds on the fatty acid residues and form oxygen bridges there . This chemical reaction links the oil molecules ( triacylglycerine ) with each other to form linoxin . The triacylglycerols each contain three fatty acid residues, as in linseed oil mainly the residues of the fatty acids α-linolenic acid and, to a lesser extent, oleic acid and linoleic acid . These then have one to three double bonds and thus offer spatial links between the individual molecules. It is therefore a form of polymerization . The curing process is not yet fully understood. With pure linseed oil, hardening takes several days, depending on the layer thickness and the substrate. Due to the catalyzing effect of the added siccatives, linseed oil varnish hardens on the surface at 20 ° C after just 24 hours.
scope of application
Corrosion protection
Due to its adhesion to the substrate, linseed oil varnish can be used to treat wood , metals and other materials. After hardening, linseed oil varnish forms a tough, elastic, water- and weather-resistant thin layer . This serves as protection against corrosion and is a wood protection for indoor and outdoor use. Because of these properties, linseed oil varnish is used in boat building and for treating furniture (table and kitchen worktops) . Since linseed oil varnish can be painted over with any varnish, it can also be used as a primer .
Manufacture of oil paints
To produce oil paints , color pigments are mixed with linseed oil varnish and finely rubbed. In turn, linseed oil is particularly suitable because of its dispersing properties. This mixture can be diluted with a little turpentine oil or white spirit to make it spreadable. Industrially manufactured oil paints usually contain other auxiliaries.
Other uses
In the production of linoleum , linseed oil varnish is an intermediate product.
In earlier times, varnish was also used to seal the seams on gas balloons in an airtight / gas-tight manner. Danish polar explorers tried to reach the North Pole with balloons prepared in this way.
Linseed oil varnish can be used on oldtimers to bind the original paint that is still rust-free but slightly peeling. After hardening, it forms a dense and solid protective layer here.
In varnish firing , linseed oil or linseed oil varnish is used to decorate and preserve ( rust protection ) metal.
When lacing of bicycles that are nipples with boiled linseed oil on the spoke fixed.
processing
Linseed oil varnish is applied to the cleaned surface. Wood should be finely sanded beforehand. The processing temperature should not be below 15 ° C, 20 ° C or more are better, as the varnish then absorbs more easily and hardens faster. If possible, you should first heat the varnish in a water bath to 35–40 ° C.
The varnish is applied wet-on-wet to wood. Several coats are made until the wood no longer absorbs the varnish. On non-absorbent surfaces, however, it should be applied as thinly as possible. Projections must be completely removed with a cloth after a pull-in time of typically half an hour to an hour. Otherwise they would cure poorly and leave a sticky surface layer.
Some types of wood, such as thuja, contain inhibitors that significantly delay oxidative hardening.
One liter of varnish is sufficient for 5 to 10 m², depending on the absorbency of the surface. When used as a primer, linseed oil varnish can also be diluted with turpentine oil . For this purpose, the substances are mixed in a ratio of 1: 1 to so-called half oil.
Self-ignition
Materials such as cloths, paper, dust or steel wool that have been wetted with linseed oil varnish should be soaked in water or kept in the absence of air as there is a risk of spontaneous combustion . There is a great danger especially with crumpled up rags, because the heat of the reaction can hardly be dissipated here.
Ecological, health and technical assessment
Stiftung Warentest rates the ecological properties of linseed oil varnish very positively:
- Energy consumption = low
- Resource consumption = low
- Environmental pollution from pollutants = low
- Durability = low
- Mendability = very good
- Disposal = good
- Health = good
The only point of criticism is the low durability due to polymerisation with aging.
See also
- Alcohol varnish
- Putty , linseed oil putty according to RAL 849 B / 2 and DIN 18545 contains linseed oil varnish
- Refreshment is made from linseed oil varnish and tar
- Linseed oil paint
Individual evidence
- ↑ Gerd Ziesemann, Martin Krampfer, Heinz Knieriemen: Natural colors, Aarau (Switzerland) 1996, ISBN 3-85502-523-1 , p. 93.
- ^ Georg Zerr: Handbook of color production. Berlin 1922, p. 819.
- ↑ German Institute for Standardization e. V., Standards Committee for Coating Materials and Coatings (NAB) in DIN: Annual Report 2010, p. 34.
- ↑ Erich Stock: Pocket book for the paint and lacquer industry as well as for the relevant trade , Stuttgart 1940, p. 357.
- ↑ a b Linseed oil and linseed oil varnish , private website for the production and use of linseed oil and linseed oil varnish, accessed on March 8, 2010.
- ↑ Kurt Wehlte: Materials and Techniques of Painting. Ravensburg 1985, ISBN 3-473-48350-8 , p. 214
- ↑ Fraunhofer Information Center for Space and Building (IRB): Linseed oil with drying process and sensitivities as well as complex varnishes ( Memento of the original from May 4, 2011 in the Internet Archive ) Info: The archive link has been inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice. , accessed March 8, 2010.
- ^ A b Armin Radünz, Andreas Lohse: Renovating: Inexpensive and environmentally friendly. Stiftung Warentest and Consumer Advice Center North Rhine-Westphalia, 2006, ISBN 978-3-937880-24-2 ; especially pp. 23, 52.
- ↑ feuerwehr-prisdorf.de: Self-ignition of linseed oil ( memento of the original from March 26, 2016 in the Internet Archive ) Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice.
