Resins and Varnishes:
Definitions, Descriptions, and Recipes
RESIN: any of a class of nonvolatile (non
evaporating), solid or semisolid organic substances obtained directly from certain plants
as exudations or prepared by polymerization of simple molecules: used in medicine and in
the making of varnishes and plastics. A substance of this type obtained from certain
Hard Resins: Fossil Resins
Tend to darken and crack with age. Must be boiled in oil to form a varnish; the use of
boiled oil mediums has led to a considerable deterioration of the paintings executed in
them and it is recommended that they be avoided by artists, though their popularity is
returning in attempts to recapture the glass like layering of past paintings.
Amber: other names: berenice, verenice, vernix, glessum (glas or glassa). a pale
yellow, sometimes reddish or brownish, fossil resin, translucent, brittle and capable of
gaining a negative electrical charge by friction. It comes chiefly from the resins of pine
trees that grew in northern Europe. These resins were gummy materials mixed with oils in
the trees. When the oils became oxidized, hard resins were left. These pine trees were
buried underground or underwater, and the resins slowly changed into irregularly shaped
lumps of amber. The largest supply of amber lies in the Baltic Sea area. It comes from a
species of pine tree that is now extinct. Some experts consider this amber the only true
amber. Central America has important deposits of amber from other sources. Most amber is
mined from a claylike soil called blue earth and was thought by the early Greeks to be a
Copal: a hard, lustrous resin obtained from various tropical trees, it has the
same recommendations as amber and nearly the same defects. The best Copal is said by
Eastlake to come from South-Africa and were imported into Europe through India. The Hard
Copal resins today come from Sierra Leone or Zanzibar. The general argument against copal,
as with other resins, is its reported tendency to darken and crack. However,
artist/investigators of this medium such as Melville Holmes argue that good quality copal
mixed as no more than 25% of the medium with a drying oil (linseed or nut) produces a good
quality paint film with no proven and documented signs of extreme yellowing or cracking
(as opposed to normal craquelure). Mixed in small quantities with oil it promotes the flow
of the paint and gives a painting lustre and brilliance, but this resin is too brittle to
be used as a varnish thinned only with Turpentine, and in its hard (semi-fossil) form is
insoluble when dry. While this insolubility makes the resin an improper choice for a final
varnish, it is precisely this feature which makes it desireable as an additive in medium.
The old "No.1 Water-white transparent" congo copal was best used, but is no
longer in production since the Belgians were driven from the Congo in the 1960s, making
the procurement of measured quality copal difficult to come by. The term copal refers to a
number of resins, from different botanical origins and chemical constitutions, from both
living (soft resin) and hard or semi hard (fossilized) sources. Therefore, copal mediums
purchased ready-made may contain unknown and variable qualities of resin, making them
susceptible to the darkening and cracking of which they have often been accused.
Soft Resins: Recent Resins
Extruded from live plants. Dissolved in cold diluent. Resoluble.
Soft Copal: Milan resin tapped from live trees can be dissolved in alcohol. Many
varieties exist of differing grades. Unlike its fossil counterpart, soft resin is
resoluble, therefore causing the same concerns as any resoluble resin when used as an
ingredient in painting medium.
Sandarac: other names: red varnish, vernix, common glas. Resin from the African
arbor vitae, known as Thuja articulata, similar to the Juniper and often referred
to by that name. It is of lower quality than amber or copal for making varnish.
Mastic: also known as white varnish. An aromatic, astringent resin obtained from
a small anarcadiaceous evergreen tree native to the Mediterranean region. Believed to have
been the resin that replaced Amber in the European's thick medium, known as Megilpe, which
was mixed with boiled linseed and litharge (huile grasse). It darkens and is more
brittle than dammar which has replaced it for creating essential oil varnishes as well as
Resin of Turpentine: also known as glorie, white resin, colophone, or concrete
turpentine. Is said to be clear and not to yellow over time. This resin in only available
as dark rosin for wood varnish today, and not recommended for fine art. see oleoresin
Dammar: a soft resin derived largely from dipterocarpaceous trees of southern
Asia and used for making colorless varnish. Any of various similar resins from trees of
other families. Due to its colorless nature and the fact that it does not harden and crack
as badly as the above listed resins, it has become the preferred resin for oil painting in
the 20th century. It is mixed with oil of Turpentine to create an essential oil varnish.
And when the dried varnish becomes soiled on the surface of the painting over time, it can
be removed again with the same essential oil of Turpentine. However, dammar becomes less
soluble with age so strong solvents may be needed for its removal when aged. Modern writer
Melville Holmes states that "Mastic and Dammar have been studied in considerable
detail by conservation scientists because of their use as picture varnishes and their
relatively rapid darkening is well documented." I have not found statements claiming
such darkening takes place when dammar is incorporated into an oil medium.
OLEORESIN: a mixture of an essential oil and a
resin, found in nature.
Common Turpentine: any of various oleoresins derived from coniferous trees, esp. the
longleaf pine, and yielding a volatile (one that readily evaporates) oil [essential oil of
Turpentine] and a resin [concrete Turpentine or rosin] when distilled. Rosin is considered
an adulterant in modern painting mediums.
BALSAMS: A turbid, viscid (sticky) , water-insoluble liquid resin. Any of
certain transparent turpentines.
Venice Turpentine: obtained from the larch Larix Europea or Larix
decidua, this is a viscous yellow liquid from which resin acids cannot be crystallized
and in this respect it differs from common turpentine. It is soluble in alcohol, ether,
acetone and turpentine but only partly soluble in petroleum hydrocarbons. When purified,
it no longer shows its natural tendency to darken a painting and produce cracks, but is
very cohesive mixed with a fixed oil. It should be used sparingly since it is resoluble,
but a little is all that is usually needed to create the desired effect of glassy sheen.
It was the most common varnish found in early recipe books and had been commonly used in
Europe at least from the time of Rubens.
The French called it Thérébenthine de Venise and said that it flowed without an
incision from conifers (meleses, pins, sapins). They said it was a golden liquid,
clear as water which thickens with age turning lemon yellow. However, in the 17th century,
common pine turpentine (rosin) was often sold as Venetian turpentine. "Large
quantities were sold with water on the top to mask the (inferior) reddish liquid
below." True Venetian Turpentine is only from the larch tree.
Strasbourg Turpentine: From the white fir abies pectinata, this is paler
than Venice turpentine and very difficult to obtain. Seventeenth-century compilers of
recipes were unanimous in preferring Strasbourg turpentine over Venice turpentine due to
its better color and odor. But both dry into desirable film when mixed with drying oils,
etc.; compared with the customary oils and varnishes, they are acceptably permanent,
nonyellowing, and durable, and tend to impart more flexibility and life to the films than
do most resins.
***When Venice or Strasbourg turpentine is mixed with stand oil, the resulting varnish is
superior for artists' mediums to the cooked oil-resin varnish group; and when liquid
driers are added, the resulting product is superior to those varnishes into which driers
have been cooked.
Canada Balsam: Said to resemble Strasbourg turpentine, Canada balsam is
relatively pure and valuable for its transparency and its high refractive index. It is
usually more expensive than Strasbourg and has been less tested.
Copaiba Balsam: of variable composition and viscosity, Copaiba balsam was found
to be impossible to remove completely and to display excessive darkening and shrinkage. It
is now avoided in picture making.
ESSENTIAL OIL: any of a class of volatile oils
obtained from plants and possessing the odor and other characteristic properties of the
plant: used chiefly in the manufacture of perfumes, flavors, and pharmaceuticals.
Examples in Painting:
Oil of Turpentine: colorless, flammable, and volatile, having a penetrating odor and a
pungent, bitter taste. Used in essential oil varnishes where it gives a matt finish, and
for thinning paints and cleaning brushes. The overuse of spirit of turpentine in thinning
oil paint will make them appear flat and dull and, reducing the binding medium, can cause
flaking due to lack of adhesion.
Spike Lavender Oil: The oil of the Lavender plant, Lavendula latifolia,
it can be used in the same ways as oil of Turpentine, but dries more slowly. Has a
"pungent odour" stronger than turpentine. Can be used to retard the drying of
oils but "it is generally felt that they do the paint films no good," according
to one writer. He may, however, have been using the oil of the female plant, known as lavenda
vera, which has a stronger odour and is used in perfumes. For painting one should use
the less aromatic oil of the male lavendula spica.
Naptha: Any of various liquids composed only of hydrogen and carbon that boil
below 450 degrees F. which are distilled from other products. Unlike the essential oils
listed above, this diluent is distilled from a mineral rather than a plant. The danger is
in its low flash point, between 20 and50 degrees F, making turpentine the preferred
solvent in modern painting.
Naptha (or Naphtha) can be made when coal tar [the pitch used by early shipbuilders
to waterproof their vessels], a sticky substance made from soft coal, is distilled. It was
the first volatile oil used to dissolve resins for varnish and considered the purest and
most unchanging diluent.
In todays terminology solvent naphtha refers to a rather impure by-product of coal tar
distillation belonging to the benzol group. It is a good solvent for coal tar and some
asphalts, but is a poor general solvent for paint and varnish materials. It is sometimes
useful for this reason, as it has little effect upon the oils and resins in an oil
painting and may be used to wash off superficial dirt, wax, etc., without the film's being
V.M.&P. Naphtha (Varnish Makers and Painters Naphtha) is a modern variety of
petroleum distillate intermediate between mineral spirits and gasoline. With a lower flash
point, a higher rate of evaporation, and usually a more disagreeable pungent odor it is
not so well suited to paint purposes as is mineral spirits.
Mineral Spirits are a petroleum distillate intermediate between Kerosene and
Gasolene (petrol) with properties similar to those of turpentine when used as a paint
thinner. It has several advantages: it leaves no sticky, gummy (resin) residue upon
evaporation, it does not deteriorate with age, its price is a small fraction of that of
gum turpentine, and it is less likely to affect persons prone to allergic reactions. It
can replace turpentine in most studio uses except in dissolving dammar.
VARNISH: a preparation for finishing or coating
wood, cloth, or other materials, consisting of resinous matter, as copal or lac, dissolved
in an oil, alcohol, or other volatile liquid. In contemporary use, the sap of certain
trees used for the same purpose.
When used in this way, oleoresinous refers to a resin dissolved by heating into a
drying oil such as linseed or walnut oil to create a thick liquid varnish.
Amber and Copal varnishes turn very dark and are red to begin with. Sandarac has the same
quality, with all eventually drying and cracking to the point of disintegration, though
Sandarac is worse than either Amber or Copal. They are all thick, dark, and slow drying.
Florentine and Sienese schools used a green underpainting in their skin tones which, when
varnished with one of these red varnishes, was neutralized, giving a proper effect to the
Mastic and Concrete Turpentine (colophone) are clearer in color, but still tend to
crack over time.
Vernice Liquida: from Berenice (amber), the constellation of Berenice's (golden)
hair. Nero referred to the golden tresses of his empress, Poppoea and Pliny observed that,
because of Poppoea, amber-colored hair became fashionable. A varnish of the middle ages
made with Amber (or Sandarac) heated and mixed with drying oil. As defined by Cardanus:
"The juice which flows from the Juniper (Thuja) is called vernix. -- From dry vernix
and linseed oil, liquid vernix is made: this is calculated to resist all effects of the
atmosphere, and therefore is applied to pictures."
Early Recipe for a thick Vernice Liquida: 3 parts linseed, 1 pt. Sandarac or
Amber, and sometimes (the white resin) concrete Turpentine was added in 2 or 3 parts. The
concrete Turpentine aids in the liquefaction of the Sandarac making the varnish lighter
and adds gloss. The recipe with Sandarac is called common vernice liquida, while that with
amber is vernice liquida e gentile. With the glossy turpentine (rosin) added, it was
especially prized for varnishing cross bows and furniture.
ESSENTIAL OIL VARNISH: a resin or balsam
dissolved in a volatile oil. Not til the close of the 15th or beginning of the 16th
century did painters use an essential oil varnish.
Examples of Varnish:
Italian Varnish: essential oil and balsam, sometimes with a resin added. Another
recipe used clear (silver) fir Turpentine (resin) mixed with an equal part naptha. It was
applied warm and is a thin, but glossy varnish.
Flemish Varnish: the Flemish sometimes used "the clearest Venice Turpentine
boiled with an equal quantity of essential oil of Turpentine." It protects from the
effects of air and moisture and can be painted over. Vandyck used 2 parts Turpentine to 1
part Venice Turpentine boiled as before and applied cool. Do not allow the essential oil
to evaporate or the Venice will not dry well and becomes too thick. This was considered
ordinary painters varnish. A retouch varnish used between layers to "oil out the
colours" was made of "essential oil of Turpentine, Spike Oil, or (naptha)
Petroleum, with (white resin of) Turpentine itself, dries at last and prevents the varnish
from cracking. Note: very little is necessary; the tenth or twelfth part." (ratio of
essential oil to resin = 10:1 or 12:1) -De Mayerne
This thin resinous film does not yellow, "undergoes no alteration... leaves a
comparatively fresh surface which takes the colour easily; and, having scarcely any body,
does not affect the superadded tints." Best used as a retouch varnish between layers
to oil out the color.
Varnish sold by Pomet in 17th century France:
1.) Spike oil, Venetian Turpentine, and Sandarac melted together to produce a
2.) Venetian varnish or White varnish -
spirits of Turpentine, Venetian Turpentine and Mastic melted together.
3.) Spirit varnish of Sandarac, Amber, Gum Elemi and Mastic with Alcohol.
4.) Common varnish - resin of Turpentine (rosin/colophone) melted with Spirit of
Some of the earliest recipes for varnish were for Venetian varnish, used to varnish and
De La Fontaine's recipe for Venetian Varnish, which was used to coat paintings, mixed 1
oz. of Venetian Turpentine with 1/2 oz. of spirits of Turpentine and boiled in a water
bath until the balsam melted. Allow to cool - but warm slightly to increase flow before
applying. Other recipes from the period are similar, though some incorporate mastic.
A mixture of mastic ground with linseed oil could be used to grind colours which would
be more resistant to the air.
Le Blond de la Tour complained that all varnishes of his day yellowed.
Modern Varnish: A retouch varnish can be made by mixing liquid Dammar varnish
with Rectified Turpentine in a ratio of 1:2. While a final varnish can be made by mixing
the same ingredients in a ratio of 2:1 or as much as 4:1. Brush on with a flat 2"
wide hogs hair bristle brush. This is the preferred artists' picture varnish for the
reasons listed above, under Resins: Dammar.
Other modern varnishes used primarily for woodworking and industrial purposes
are made using Lac, a resinous substance deposited on the twigs of various trees in
southern Asia by the female of the Lac insect. Shellac is lac that has been
purified and formed into thin sheets, used for making varnish, or a varnish made by
dissolving this material in alcohol or a similar solvent.
Shellac tends to turn dark and to crack with age and is therefore not to be used as a
retouch or final varnish. But White or Orange grade Shellac can be thinned with alcohol to
a watery consistency to be applied as an isolating varnish, or thin size, over a
preliminary oil wash underpainting. The alcohol used should be ethyl, or grain, alcohol.
Pure Grain Alcohol is 94% pure alcohol and 6% water, while Anhydrous or Absolute Ethyl
Alcohol is 100% alcohol. Either will work to mix an extremely thin solution of shellac
that can be used as a sizing for porous surfaces and as an isolating layer between films
of paint in tempera painting. Or it can be applied just thickly enough over a wash drawing
or underpainting in oils to seal the image, make the surface less absorbent and give it
tooth for the adhesion of the body painting over it. Since it is not soluble in turpentine
or mineral spirits it can protect a paint layer from further solvents in the overpainting.
The drawback is that alcohol (shellac's solvent) can have a destructive effect on oil
paint layers and, after the alcohol has evaporated, any layer of shellac must be
completely covered in pigmented layers which may be contrary to the desired effect in the
painting. Perhaps a safer and more flexible method is to seal an ink drawing on gesso with
a glue size or to add a thin coat of damar retouch varnish between layers on canvas.
Lacquer: a protective coating consisting of a resin, cellulose ester, or both,
dissolved in a volatile solvent, sometimes with pigment added. Any of various resinous
varnishes, esp. one obtained from a Japanese tree, Rhus verniciflua, used to
produce a highly polished, lustrous surface on wood or the like.
Ester: a compound produced by the reaction between an acid and an alcohol with
the elimination of a molecule of water, as ethyl acetate or dimethyl sulfate.
Cellulose: an inert carbohydrate, the chief constituent of the cell walls of
plants, wood, cotton, hemp, paper, etc.
Pure Methacrylate, or acrylic, solution in mineral spirits has been accepted by
museum and technical specialists since the early 1930s. It is colorless and dries to a
dull satiny finish, often preferred to the higher gloss of damar. This is best used on
light colored, or "blonde", works of art since dark pictures may be made to look
grayish by matt varnishes. Acrylic's great flexibility may allow it to be applied to
paintings that have not cured if a work must be shipped out of the studio prematurely.
A pure solution of Polycyclohexanone (keytone) in mineral spirits may be better
suited for dark images as it dries very closely to the gloss of damar and has been used
since the 1950s.
These are best used as final varnishes on oil paintings since they can be easily
removed with mineral spirits. One disadvantage of the synthetic varnishes is their
tendency to form films that are softer, with tendencies to attract dirt and dust to a
greater extent than damar, thus potentially requiring more frequent cleaning. And their
softer films may not protect the painting surface from abuse and scratches as well as the
History, Definitions, and Techniques | Drying Oils and Mediums
Resins and Varnishes | Pigments
Past |Pigment Chemistry
Supports for Painting | Grounds on Canvas
| Techniques of Past Masters
Discussion with National Gallery Conservator
Info from: SANDERS-STUDIOS.COM