SUMAC

GENERALITIES

There are various species of Sumac, a small tree found in Mediterranean areas. The most valuable for tanning purpose is the one cultivated in South Europe called « Rhus Coriaria ». With Chestnut, it is the only tan of industrialised countries origin.

Rhus Coraria

The harvest is made in Summer when the leaves start to be reddish. On one acre, 10,000 trees can grow, giving 800 Kg of dry leaves.

HISTORY

Sumac is one of the noblest and most ancient tanning material of the Mediterranean world. It was used by Egyptian and Greek during Antiquity as a wool dye and later as a tan extract.
The botanic name of Sumac comes from the Antic Roman tanner called « Coriarii » in latin language.
Cultivated in the Middle Age by Arabs in Palestine, this extract has made the glory and wealth of tanners producing genuine Morocco and Cordovan leather.
Nowadays, Sumac is mainly used by tanneries producing high valuable furniture and bag items.

COMPOSITION

Sumac belongs to the pyrogallic family. The leaves contain around 30 % of a tan which is the condensation of gallic, digallic acid with glucose.

Extraction of Sumac’s tan is very particular compared to other vegetable extracts as it is very sensitive to heat (decomposition into gallic acid). It is the reason why only few manufacturers are able to offer a Sumac extract unaltered by oxidation with a concentration of tan from 56 to 62 % after spraydrying.
The impurities forwarded are free gallic acid, glucose, greenish dye (Chlorophyl), inorganic salt. All these compounds give interesting properties, except salt like iron oxide which has to be stripped out to avoid patchiness.

PROPERTIES

Compared to all other vegetable tans except Tara, Sumac has excellent light fastness certainly due to the strong antioxidation nature of gallic group.
When used alone, yellow-greenish leather is obtained with a very light weight, smooth grain and unusual softness for a full vegetable tanning.
These particularities could be of some interest for the technician who would like to develope special articles with natural extracts.
For example, due to gallic acid group, Sumac gives a slightly reversible tannage on the surface of the leather. This is an excellent property comparable to the action of naphtalene based syntans.
By adding Sumac 10-15’ prior to the dye, better uniformity, faster penetration are possible. With most of the black dyes which are of blue tone, it enhances the jetness because of its own yellowish shade. Contrary to syntans, we can note that Sumac has no bleaching effect and it increases the burnishability of leather.
Another advantage is its high affinity with basic dyes allowing irreversible complex firmly fixed on the grain side, giving good dry rub fastness on nubuck and suede. By using Sumac with cationic fatliquor, two way nap effect and high shine appear.
Apart from dye’s auxilialy, Sumac could be interesting in upholstery, automotive and articles which need to be light weight, thin and soft..
It is commonly used for lining and bookbinding because of its excellent perspiration and light fastness.
As all vegetable tan, Sumac enhances glazability and because of glucoside and antioxydation property of gallic acid, it prevents the grain side from cracking and improves the tear resistance of vegetable leather after ageing.

COMMERCIAL BRANDS

RETAN BLK-M
Ground Sumac, micronized and purified. It gives a strong tea smell to leather. When used for the production of shrunken and bold grain, the strong deshydration given by latest action of gallic acid and absorption by the insoluble parts of the grounded powder provoke an uniform, flat, shrunken grain on the pelt.
RETAN BLK-M could be used for hard grain Morocco leather and as a substitute to grounded Tara and Myrobolam when pleasant smell and high dyeing uniformity are needed.

RETAN K19
It is the most common in the Market because of its fairly high tan content - around 58 % - and its versatility. It can be used with all other vegetable and syntan without special care.

RETAN BL, liquid
Unaltered Sumac of the best origin. Its medium astringency and nominal percentage of insoluble make this extract specially recommended as a dye auxiliary and for the manufacture of thin, soft leather of high value. RETAN BL is also used for the tannage of reptile and crocodile.

RETAN TSK
It is the best Sumac for tanners processing small skins like goat, sheep with a pure aniline finish. Grain of such skins retanned with « TSK » remain flat with a mellow touch.
RETAN TSK is also used as dye mordant on leather, textile, nylon and cotton.