Editing Varnish (section)

==Types==

===Violin===
[[File:German, maple Violin.JPG|thumb|Varnished violin]]
[[Violin]] varnishing is a multi-step process involving some or all of the following: primer, sealer, ground, color coats, and clear topcoat. Some systems use a drying oil varnish as described below, while others use spirit varnish made of resin(s) dissolved in alcohol. Touchup in repair or restoration is only done with solvent based varnish.

Drying oil such as walnut oil or linseed oil may be used in combination with [[amber]], [[copal]], [[rosin]] or other [[resin]]s. Traditionally the oil is prepared by cooking or exposure to air and sunlight, but modern [[stand oil]] is prepared by heating oil at high temperature without oxygen. The refined resin is sometimes available as a translucent solid and is then "run" by cooking or melting it in a pot over heat without solvents. The thickened oil and prepared resin are then cooked together and thinned with turpentine (away from open flame) into a brushable [[Solution (chemistry)|solution]]. The ingredients and processes of violin varnish are very diverse, with some highly regarded old examples showing defects (e.g. cracking, crazing) associated with incompatible varnish components.

Some violin finishing systems use vernice bianca (egg white and gum arabic) as a sealer or ground. There is also evidence that finely powdered minerals, possibly volcanic ash, were used in some grounds. Some violins made in the late 18th century used ox blood to create a very deep-red coloration. Today this varnish would have faded and currently be a very warm, dark orange.<ref>[1793 johann baptist havelka]</ref>

===Resin===
Most resin or gum varnishes consist of a natural, plant- or insect-derived substance dissolved in a solvent, called ''spirit varnish'' or ''solvent varnish.''<ref>{{cite book |editor1-last=Patrick |editor1-first=David |title=Chambers's Encyclopaedia: A Dictionary of Universal Knowledge |date=1892 |publisher=William & Roberts Chambers |location=Edinburgh |page=430 |url=https://books.google.com/books?id=v2gWAAAAYAAJ |language=en}}</ref> The solvent may be [[ethanol|alcohol]], turpentine, or [[petroleum]]-based. Some resins are soluble in both alcohol and turpentine. Generally, petroleum solvents, i.e. [[mineral spirits]] or [[paint thinner]], can substitute for turpentine. The resins include [[amber]], [[dammar]], [[copal]], [[rosin]], [[sandarac]], [[elemi]], [[Benzoin (resin)|benzoin]], [[Mastic (plant resin)|mastic]], [[balsam]], [[shellac]], and a multitude of [[lacquer]]s.

[[Chemical synthesis|Synthetic]] resins such as [[phenolic resin]] may be employed as a secondary component in certain varnishes and paints.

Over centuries, many recipes were developed which involved the combination of resins, oils, and other ingredients such as certain [[waxes]]. These were believed to impart special tonal qualities to musical instruments and thus were sometimes carefully guarded secrets. The interaction of different ingredients is difficult to predict or reproduce, so expert finishers were often prized professionals.

===Shellac===
{{Main|Shellac}}
Shellac is a very widely used single-component resin varnish that is alcohol-soluble. It is not used for outdoor surfaces or where it will come into repeated contact with water, such as around a sink or bathtub. The source of shellac resin is a brittle or flaky secretion of the female [[Kerriidae|lac]] insect, ''[[Kerria lacca]]'', found in the forests of [[Assam]] and [[Thailand]] and harvested from the bark of the trees where she deposits it to provide a sticky hold on the trunk. Shellac is the basis of [[French polish]], which for centuries has been the preferred finish for fine furniture. Specified "dewaxed" shellac has been processed to remove the waxy substances from original shellac and can be used as a [[Primer (paint)|primer]] and sanding-sealer substrate for other finishes such as polyurethanes, alkyds, oils, and acrylics.

Prepared shellac is typically available in "clear" and "amber" (or "orange") varieties, generally as "three-pound cut" or three pounds dry shellac to one US gallon of alcohol. Other natural color shades such as ruby and yellow are available from specialty pigment or woodworker's supply outlets. Dry shellac is available as refined flakes, "sticklac," "button lac," or "seedlac." "White pigmented" shellac primer paint is widely available in retail outlets, billed as a fast-drying interior primer "problem solver", in that it adheres to a variety of surfaces and seals off odors and smoke stains. Shellac clean-up may be done either with pure alcohol or with [[ammonia]] cleansers.

===Alkyd===
{{main| Alkyd}}
Modern commercially produced varnishes employ some form of [[alkyd]] for producing a protective film. Alkyds have good solvent, moisture and UV light resistance. Alkyds are chemically modified vegetable oils which operate well in a wide range of conditions and can be engineered to speed up the cure rate and thus harden faster.<ref>{{Cite web |title=Alkyd - an overview {{!}} ScienceDirect Topics |url=https://www.sciencedirect.com/topics/chemistry/alkyd |access-date=2022-04-12 |website=www.sciencedirect.com}}</ref> Usually this is by the use of metal salt driers such as [[cobalt]] salts.<ref>{{Cite news |title=Driers for Alkyd Coatings - an Overview |url=https://www.pcimag.com/articles/92835-driers-for-alkyd-coatings-an-overview |access-date=2022-04-12 |website=www.pcimag.com |language=en}}</ref><ref>{{Cite web|title=Cobalt Drier for Paints {{!}} Cobalt Cem-All®|url=https://www.borchers.com/product/12-cobalt-cem-all/|access-date=2021-05-15|website=Borchers|language=en-US}}</ref> Better (and more expensive) exterior varnishes employ alkyds made from high performance oils and contain [[Ultraviolet|UV]]-absorbers; this improves gloss-retention and extends the lifetime of the finish. Various resins may also be combined with alkyds as part of the formula for typical "oil" varnishes that are commercially available.

===Spar varnish===
''[[Spar varnish]]'' (also called ''marine varnish'' or ''yacht varnish'') was originally intended for use on [[ship]] or [[boat]] [[spar (sailing)|spar]]s, to protect the timber from the effects of sea and weather. Spars bend under the load of their sails. The primary requirements were water resistance and also [[elasticity (physics)|elasticity]], so as to remain adhering as the spars flexed. Elasticity was a pre-condition for weatherproofing too, as a finish that cracked would then allow water through, even if the remaining film was impermeable. Appearance and gloss was of relatively low value. Modified [[tung oil]] and [[phenolic resin]]s are often used.

When first developed, no varnishes had good [[Ultraviolet|UV]]-resistance. Even after more modern synthetic resins did become resistant, a true spar varnish maintained its elasticity above other virtues, even if this required a compromise in its UV-resistance. Spar varnishes are thus ''not'' necessarily the best choice for outdoor woodwork that does not need to bend in service.

Despite this, the widespread perception of "marine products" as "tough" led to domestic outdoor varnishes being [[brand]]ed as "Spar varnish" and sold on the virtue of their weather- and UV-resistance. These claims may be more or less realistic, depending on individual products. Only relatively recently have spar varnishes been available that can offer both effective elasticity and UV-resistance.

===Drying oils===
{{main| Drying oil}}
Drying oils, such as [[linseed oil|linseed]] and [[tung oil]], are not true varnishes though often in modern terms they accomplish the same thing.

===Polyurethane===
{{main| Polyurethane}}
[[File:Polyurethane varnished table.jpg|left|thumb|A table green wood-stained and varnished with three layers of polyurethane varnish]]
[[Polyurethane]] varnishes are typically hard, abrasion-resistant, and durable coatings. They are popular for [[hardwood]] floors but are considered by some wood finishers to be difficult or unsuitable for finishing furniture or other detailed pieces. Polyurethanes are comparable in hardness to certain alkyds but generally form a tougher film. Compared to simple oil or shellac varnishes, polyurethane varnish forms a harder, decidedly tougher and more waterproof film. However, a thick film of ordinary polyurethane may de-laminate if subjected to heat or shock, fracturing the film and leaving white patches. This tendency increases with long exposure to sunlight or when it is applied over soft woods like [[pine]]. This is also in part due to polyurethane's lesser penetration into the wood. Various priming techniques are employed to overcome this problem, including the use of certain oil varnishes, specified "dewaxed" shellac, clear penetrating [[epoxy]] sealer, or "oil-modified" polyurethane designed for the purpose. Polyurethane varnish may also lack the "hand-rubbed" lustre of drying oils such as linseed or tung oil; in contrast, however, it is capable of a much faster and higher film build,  accomplishing in two coats what may require multiple applications of oil. Polyurethane may also be applied over a straight oil finish, but because of the relatively slow curing time of oils, the emission of certain chemical byproducts, and the need for exposure to oxygen from the air, care must be taken that the oils are sufficiently cured to accept the polyurethane. One of the disadvantages of a polyurethane-based varnish is the tendency to yellow over time. This is because the hydroxyl groups of a regular alkyd are reacted with [[Toluene diisocyanate|TDI]] to produce a urethane-alkyd. This introduces a high degree of aromaticity and hence tendency to yellow.<ref>{{Cite web |title=Development of Low-Color Alkyd Resins with High Content of Biobased Succinic Acid |url=https://www.pcimag.com/articles/99678-development-of-low-color-alkyd-resins-with-high-content-of-biobased-succinic-acid |access-date=2022-04-12 |website=www.pcimag.com |language=en}}</ref> 

Unlike drying oils and alkyds which cure after evaporation of the solvent and upon reaction with oxygen from the air, true polyurethane coatings cure after [[evaporation]] of the solvent and then either by a variety of reactions of [[chemical]]s within the original mix, or by reaction with [[moisture]] from the air. Certain polyurethane products are "hybrids" and combine different aspects of their parent components. "Oil-modified" polyurethanes, whether water-borne or solvent-borne, are currently the most widely used wood floor finishes.

Exterior use of polyurethane varnish may be problematic due to its heightened susceptibility to deterioration through [[ultra-violet]] light exposure. All clear or translucent varnishes, and indeed all [[film]]-[[polymer]] coatings (e.g. paint, [[wood stain|stain]], epoxy, synthetic [[plastic]], etc.) are susceptible to this damage in varying degrees. [[Pigment]]s in paints and stains protect against UV damage. UV-absorbers are added to polyurethane and other varnishes (e.g. spar varnish) to work against UV damage but are decreasingly effective over the course of 2–4 years, depending on the quantity and quality of UV-absorbers added, as well as the severity and duration of sun exposure. Water exposure, humidity, temperature extremes, and other environmental factors affect all finishes.<ref>{{Cite journal |last1=Pereira |first1=Fabíola Manhas Verbi |last2=Bueno |first2=Maria Izabel Maretti Silveira |date=2009-12-01 |title=Evaluation of varnish and paint films using digital image processing, energy dispersive X-ray fluorescence spectrometry, and chemometric tools |url=https://doi.org/10.1007/s11998-009-9165-5 |journal=Journal of Coatings Technology and Research |language=en |volume=6 |issue=4 |pages=445–455 |doi=10.1007/s11998-009-9165-5 |s2cid=136875063 |issn=1935-3804 |access-date=2023-03-14 |archive-date=2023-03-14 |archive-url=https://web.archive.org/web/20230314202630/https://link.springer.com/article/10.1007/s11998-009-9165-5 |url-status=live |url-access=subscription }}</ref>

===Lacquer===
{{Main|Lacquer}}
The word ''lacquer'' refers to quick-drying, solvent-based varnishes or paints. Although their names may be similarly derived, lacquer is not the same as ''[[shellac]]'' and is not dissolved in alcohol. Lacquer is dissolved in lacquer thinner, which is a highly flammable solvent typically containing [[butyl acetate]] and [[xylene]] or [[toluene]]. Lacquer is typically sprayed on, within a ''[[spray booth]]'' that evacuates overspray and minimizes the risk of combustion.

The rule of thumb is that a clear wood finish formulated to be sprayed is a lacquer, but if it is formulated to be brushed on then it is a varnish. Thus, by far most pieces of wooden furniture are lacquered.{{Citation needed|date=March 2017}}
 
Lacquer may be considered different from varnish because it can be re-dissolved later by a solvent (such as the one it was dissolved in when it was applied) and does not chemically change to a solid like other varnishes.<ref>{{cite web|url=http://www.johnsankey.ca/pine.html|title=Finishing Solid Pine|website=www.johnsankey.ca}}</ref>

===Acrylic===
[[Acrylic resin]] varnishes are typically water-borne varnishes with the lowest [[refractive index]] of all finishes<ref>{{Cite journal |last=de la Rie |first=E. René |date=1987 |title=The Influence of Varnishes on the Appearance of Paintings |url=https://www.jstor.org/stable/1506186 |journal=Studies in Conservation |volume=32 |issue=1 |pages=1–13 |doi=10.2307/1506186 |jstor=1506186 |issn=0039-3630|url-access=subscription }}</ref> and high transparency. They resist yellowing. Acrylics have the advantage of water clean-up and lack of solvent fumes, but typically do not penetrate into wood as well as oils. They sometimes lack the brushability and self-leveling qualities of solvent-based varnishes. Generally they have good UV-resistance.

In the art world, varnishes offer dust-resistance and a harder surface than bare paint – they sometimes have the benefit of ultraviolet light resistors, which help protect artwork from fading in exposure to light. Acrylic varnish should be applied using an isolation coat (a permanent, protective barrier between the painting and the varnish, preferably a soft, glossy gel medium) to make varnish removal and overall conservation easier. Acrylic varnishes used for such a final removable art protection layer are typically mineral-spirit–based acrylic, rather than water-based.

===Two-part epoxy===
{{main| Epoxy}}
Various [[epoxy]] resin systems have been formulated as varnishes or floor finishes whereby two components are mixed directly before application.<ref>{{Cite web|last=Blue & Green Tomorrow|date=2016-03-04|title=Understanding the Pros and Cons of Epoxy Floors|url=https://blueandgreentomorrow.com/spend/understanding-pros-cons-epoxy-floors/|access-date=2021-05-14|website=Blue and Green Tomorrow|language=en-US}}</ref> Sometimes, the two parts are of equal volume and referred to as 1:1 but not always, as 2:1, 3:1, 4:1 and even 5:1 mixing ratios are commercially available. The individual components are usually referred to as Part A and Part B. All two-part epoxies have a pot-life or working time during which the mixed material can be used. Usually the pot-life is a matter of a few hours or less, but this is highly temperature dependent. Both water-borne and solvent-based epoxies are used. Epoxies do have a tendency to yellow over a fairly short period of time.<ref>{{Cite journal |last1=Krauklis |first1=Andrey E. |last2=Echtermeyer |first2=Andreas T. |date=September 2018 |title=Mechanism of Yellowing: Carbonyl Formation during Hygrothermal Aging in a Common Amine Epoxy |journal=Polymers |language=en |volume=10 |issue=9 |pages=1017 |doi=10.3390/polym10091017 |pmid=30960942 |pmc=6403735 |issn=2073-4360|doi-access=free }}</ref>

===Conversion===
Used when a fast-curing, tough, hard finish is desired, such as for kitchen cabinets and office furniture. Comes in two parts: a resin and an acid catalyst. The first is a blend of an amino resin and an alkyd. The acid catalyst is added right before application in a set ratio determined by the manufacturer. Most produce minimal yellowing. There are, however, two downsides to this finish. The first is that as the finish cures, it gives off [[formaldehyde]], which is toxic and carcinogenic. The second is that the finish can crack or craze if too many coats are applied.