They represent the biggest group of the finished leathers. The grown final layer of the corium, the grain structure characteristic for the specific animal and the aditionally possible dying and the application of finishing components allow the full-grain to match all requirements set for the product leather. It is further distinguished subject to the production method:
Many types of leathers are finished after the tannage without further dying operations. These leathers show the characteristic colour for the relevant tanning method. They are still today called natural or natural coloured leathers as they are leathers traditionally tanned with vegetable tanning agents. Next to the big group of sole leathers are to be added the russet upper leather, the blank leather etc. as long as the last mentioned are not been dyed additionally. Also the various groups of intermediate producs, called crusts are mostly marketed „natural“ independent of the tanning method and in the un-dyed state also called „ross“. Un-dyed crust leathers can be marketed as natural crust or dyed crust whereas the term “ross” always the un-dyed version indicates.
These are leathers that are dyed after the tanning processes during the wet-finishing with soluble dyestuffs. The dyestuffs can be absorbed and bound by the leather fibers either by pickling the leather in the dye-float (e.g. in the drum) or by applying a concentrated dye-float onto the surface(s) – the head-dying. The grain surface of the leathers is freely visible and has the natural look. However, with that goes also that variances in the grain (natural characteristics and damages) may be existing like some slight irregularities of the surface colour (valid for natural as well as aniline leather.
The term “aniline” refers for leather to the transparent dying with dyestuffs that does not result in a coverage of the visible hair holes or the surface and do not cover the natural grain pattern / pore pattern or the natural surface. Attempts to replace the use of the term “aniline” for leather by e.g. „natural state leather“ in order to avoid any mixing up with the blood poison Aniline have failed due to the firm establishment of this term in the vernacular as a synonym for a transparent dyeing. The term aniline or aniline leather is therefore still today a traditionally firmly established technical term in the German language as well as in the relevant translations into other languages.
Finished leathers are distinguished according to following groups:
Finished, full-grain leathers
finished, corrected leathers
corrected buffed leathers
Finished full-grain leathers have a top layer that can vary in thickness, subject to the requirements and can be dyed with more or less soluble dyestuff or pigments. The transition from an aniline leather to a slightly dressed leather with an aniline character and to semi-aniline leathers that are slightly dressed through the use of small amounts of pigments has to be considered as flowing. Decisive is that the natural grain pattern is not obstructed till the semi-aniline. The existing finish on the leather can easily be recognized with a magnifier (linen tester) with six to ten times enlargement. The hair root holes are in most cases partially to fully covered by the finish. The behaviour against various solvents can serve as a pre-orientation for the identification of the finish. Cellulose-nitrate and binder finishes can be removed by rubbing with a cloth wetted with an organic solvent (e.g. acetone), albumin or casein finishes are rubbed off with a diluted ammonia solution. Cross-linked polyurethane finishes on the leather can hardly be affected. They will hardly show any change after rubbing with the mentioned solvents. Those leathers mentioned in this point, which are called full-grains, must either have a completely undamaged grain or, if corresponding agreements exist, have to have distinctly recognizable remnants of the hair pores.
Finished corrected respectively grain-corrected full-grain leathers: the shift is here also flowing. To correct means that certain grain irregularities (e.g. by healed scars, dung damage) are equalized through the slight buffing of the grain. In this case should also remnants of the hair pores be visible when checked under a six to ten times magnifying glass.
Buffed, finished leathers do in most cases not have any grain layer left. The treatment has been much deeper. The more the grain is buffed or removed the thicker and more compact has the finish to be as the leather surface has to be created virtually completely new.