Sharpening history. GOI polishing paste

GOI (ГОИ) pastes — grinding and polishing compounds made based on chromium (III) oxide. They are used for grinding and polishing steel, non-ferrous metal alloys, plastics and polymers, optical glasses, ceramics, etc. They were developed in 1931-1933 by Soviet scientists, employees of the State Optical Institute. The objectives of the development of the paste were: protection of surfaces from environmental influences, restoration of damaged surfaces, and improvement of their reflective properties.

The manufacturer of the famous paste - the State Optical Institute was founded in 1918. The main focus of the Institute's work was the development of optical science and instrument engineering. The main directions during the hundred years of its existence were atomic and molecular spectroscopy, the study of luminescence, photochemistry, computational optics, nonlinear optics, microscopy, astronomical optics, etc. In recent years, the institute was transformed into a joint-stock company "State Optical Institute". named after S. I. Vavilov". And then it became the head scientific organization of the holding company JSC "Shvabe" of the State Corporation Rostekh.

The main component of GOI paste is one of the chromium oxides, that is, the chemical compound of chromium and oxygen. Chromium oxides are divided into several types: chromium (II) oxide - CrO, chromium (III) oxide - Cr2O3, chromium (IV) oxide - CrO2, chromium (VI) oxide - CrO3.  Cr2O3 is a form of chromium oxides that forms a solid, refractory powder of green color. The melting point of the oxide is 2435 °C, the boiling point is about 4000 °C. The density is 5.21 g/cm3, it is not soluble in water. In hardness, it is close to corundum (aluminum oxide), so it is introduced into the composition of polishing agents. It is the main pigment for green paint. An important component for magnesia refractories and thermite mixtures, a catalyst for organic reactions.  As an abrasive, it is used as the main component of polishing pastes (for example, GOI). Initially, the paste was developed for grinding glasses and lenses. Today, it is used by jewelers for processing precious metals, car mechanics for polishing car glasses and headlights, etc.

GOI paste consists of a plastic mass of green color. It is a fine-grained granular powder. In addition, the paste contains organic solvents and chemical reagents: kerosene, stearin, fat, etc. The granularity of the paste depends on the ratio of these substances and the size of the abrasive particles.

The paste is divided into four numbers:

 No. 1 – Black paste with a green hue, with a grain size of 0.3-0.1 microns. The paste consists of 65-70 % trivalent chromium oxide. It is intended for the most delicate surface treatment, in fact, the effect of processing with such a paste is expressed only in creating a gloss on the surface.

 No. 2 - Dark green paste, with a grain size of 7-1 microns.  The paste consists of 65-74% parts of trivalent chromium oxide. Is suitable for fine polishing.

 No. 3 - Green paste, with a grain size of 17-8 microns. The paste consists of 65-70 % trivalent chromium oxide. The paste is designed for grinding and removing small scratches.

 No. 4 - Light green paste, with a grain size of 40-18 microns. The paste is composed of 75-85% of the parts of the trivalent chromium oxide. This is the coarsest of the GOI pastes. Intended for rough surface grinding and scratch removal. As a result, it gives a matte surface.

The abrasive ability of GOI paste in laboratory conditions is determined by the thickness of the metal removed from the steel plate 9 × 35 mm when it passes a path of 40 m on a cast-iron plate 400×400 mm.

The paste is available in the form of solid bars and a jar in the form of a viscous mass. It has a fairly high density, which increases with prolonged storage of the paste. Therefore, before starting work, the paste must be softened. For this purpose, liquid machine oil, oil for sewing machines, and similar coolants are used. For the softening process, the amount necessary for the work is broken off from the main piece of paste and kneaded together with the oil. The resulting mixture should be mixed well and only when a homogeneous mass is obtained, use it in the work.

Traditionally, during the Soviet era, GOI paste was used as a finishing tool for knives and razors. To do this, it was applied to a strop for straightening razors or to a leather belt. Most often, this was done after sharpening the knife on a water stone made of silicon carbide. In the process of such fine-tuning, the secondary bevel acquired a shine and a mirror surface. However, due to the insufficient hardness of the belt, a noticeable lens appeared on the knife, and the symmetry of the sharpening angles was not observed. The most rational and safe way to maintain the sharpening angle was considered another method of applying the paste. Sandpaper of 1200 grit was glued on a wooden board with GOI paste No. 3 applied on top of the paper. This method of finishing sharpening was effective for the most common then, relatively soft steels, such as 40x13 and 95x18. The main disadvantage of finishing with GOI paste is the difficulty in selecting the amount of paste and the degree of viscosity of its consistency. Besides, the paste in the process of sharpening tended to collect all the small particles, dust, including metal ones, the remains of sludge from the main sharpening, which often caused parasitic marks on the secondary bevel.

From the point of view of safety, GOI paste also had obvious drawbacks.  Chromium (III) oxide is toxic and can cause dermatitis if it gets on the skin. According to Russian standards, it has a class 3 hazard, the maximum single MPC (maximum permissible concentration) in the air of the working area is 1 mg/m3, the oxide can cause allergies. To work with the paste, it is recommended to use gloves, safety glasses, and when using a grinding wheel or other equipment — a respirator or mask and protective clothing, as the paste particles or dust can fly that can not be inhaled, and which is quite poorly cleaned from clothing.  After working with the paste, it is necessary to wash your hands with soap and treat the knife blade before contact with food.

GOI paste at the time of its creation was one of the most modern and effective materials for polishing. However, at the moment, using it for the finishing knives is not the best choice. Diamond polishing compounds and Luxor and Dialux aluminum oxide-based pastes are ahead of it in terms of efficiency and productivity.