Medium-hard resins

Sandarak

A resin secreted by the trees of North Africa (Morocco, Algiers).
It occurs in the form of elongated droplets with a yellowish color and a glassy turn.
Brittle, similar to kauri copal in terms of hardness.
Melting point 145 ÷ 148°C.
It is soluble in alcohol, ether, lavender and spik oil.
In the past, sandarak was called juniper or pine gum.
Sandarak was sometimes used for tempera as a final or interlayer varnish.
Although sandarak varnishes do not yellow very much, they are, however, among the inferior to mastic (brittle).
Sandarak belongs to the acidic resins.

Mastic (mastic resin).

The best mastic species are Bombay mastic, East African mastic and East Indian mastic.
Light yellow, drop-shaped.
Matte surface, glossy in the breakthrough.
It softens in the fingers, under the pressure of the teeth it does not crumble, but clumps.
In terms of hardness it is intermediate between sandarak and damara.
It softens at 90°C, melts at 105 ÷ 120°C.
It dissolves easily in turpentine, ether and benzene. Before use, it should be pulverized and slightly heated to lose moisture.
Mastic dissolved in turpentine or toluene is used as a varnish for paintings.
It has a tendency to crack and darken.
It belongs to the neutral resins.

Damara

Resin of subtropical deciduous trees (India, Ceylon, Burma, Indochina, Sumatra, Philippines). The most popular varieties are singapore and batavia.
It dissolves best in turpentine.
It should be dried well before dissolving, as it contains a lot of moisture and, like manilla copal, becomes cloudy from moisture in the varnish. The entire varnish then becomes cloudy and unusable.
Damara varnish is colorless for a long time and does not yellow as quickly as other varnishes.
Damara dissolved in oil can be used as a varnish for painting.
It belongs to neutral resins. It melts at a temperature of 100 ÷ 150°C.

Rosin

It is obtained during the production of turpentine.
The color ranges from light yellow to brown. Soft, brittle, melts at 75 ÷ 78°C. Acidic. Dissolves in spirit, acetone, turpentine, toluene and in alkalis, forming resin soaps.
In painting it has no use - abietic acid reacts with some dyes.
Thanks to the acid reaction, it is irreplaceable in the production of siccatives.

Shellac

An exotic resin. In its raw state it is red. It is used in the production of red paint.
It contains 75% resin, 5% wax and 6% dye.
Yellow, in thin leaves.
Dissolves in spirit, borax or in strong alkalis.
With ammonia, when heated, it gives water-based varnishes.
It differs from other resins in that it does not dissolve in drying oils, since it does not contain resin acids, but fatty acids.
It melts at 100 ÷ 115°C.
Shellac rebounds, but darkens from air.
It should be stored in water.

Balsams

Resins that occur in a semi-liquid or liquid state are called balsams. They are a natural solution of resins in volatile plant oils.
Some of the oils contained in balsams belong to volatile hydrocarbons, while others are non-volatile.
Resins included in balsams can be extracted artificially, with resins of different degrees of hardness obtained from different balsams. All resins obtained by this method belong to soft resins.
Balsam is a thick liquid secreted by some trees, especially pin trees.
Balsams do not combine with water, but give connections with oil and solvents used in the manufacture of paints and varnishes.
Depending on their origin, balsams vary in consistency, color and transparency. As a result of volatile oils volatilizing from them, lotions thicken, and some even harden after a while.
The main components of balsams are abietic acid and pimaric acid, as well as resins (resinates) in a minor part.

Copaura balsam

It comes from Capaifera trees (South America). It is a solution of soft resin in volatile oil (40 ÷ 90%).
Varieties:

• Macariba - dense.
• Para - rarer.

Pale yellow color, characteristic smell, bitter taste.
On glass it dries in four days forming a hard and smooth film.
It is a very good additive to oil paints and contributes to their even drying. It is resistant to moisture.
It is used to regenerate old varnishes (Petenkoffer method).
When dry, it belongs to hard but brittle resins.

Canada balsam

Takes from the seeps of fir and other varieties. Colorless and transparent. Boiling point 150°C. After hardening, it does not crystallize or blacken (it is sometimes used to glue glass).
It is soluble in many types of solvents and in oils. It belongs to the natural varnishes of painters.
Added to oil paints, it does not blacken them, but gives a good consistency and partially stops them from drying.

Venetian turpentine

Takes its name from the Austrian larch tree. Used for lasering binders as early as the Renaissance.
A thick, colorless, transparent liquid. It has a lemony odor and does not crystallize.
After standing for a while, it acquires a faint bluish fluorescence.
It is soluble in alcohol, acetone, chloroform, turpentine and toluene.

Strasburg turpentine

Obtained from silver Tyrolean spruce. It smells of lemon. Bitter taste.
More liquid and better drying than Venetian turpentine.
It has all the advantages of Venetian turpentine. Widely used in the 16th century, known in ancient times.
If Venetian or Strasbourg turpentine is mixed with oil, the varnish obtained by this method is superior to the group of varnishes made from resins boiled in oil.