Raw materials required to make a telescopic mirror.

RONCHI

Ronchi Screens or Ronchi Gratings have been used for many years as a quick qualitative method to evaluate overall mirror surface smoothness and figure. We stock a series of 7 gratings: 50, 75, 100, 125, 150, 175, and 200 lines per inch with equally spaced opaque lines that occupy 50 percent of the total area. The grating is a highly accurate photographic reproduction on a thin, transparent, and durable film. The thin film base minimizes annoying diffraction effect common to thick glass substrates.

Silicon Carbide

Very sharp and long lasting to help you form your curve fast and accurately.

You can rely on India Astronomy Club - IAC optical grade abrasives because they are accurately graded to ensure that no larger, scratch producing sizes or foreign materials are present. Further, special processing steps are used to produce abrasive grains of like shape and edge for longer and more economical grinding action. There are many different ways to designate abrasive sizes. We uses two — Grit and Micron sizing. A one micron size abrasive particle measures one millionth of a meter. Silicon Carbide Very sharp and long lasting to help you form your curve fast and accurately.

Silicon carbide is an extremely sharp, synthetic abrasive which approaches the diamond in hardness. It is made by mixing finely ground petroleum coke with pure glass sand. The mixture is loaded into a crucible and heated by electric arc to temperatures in excess of 2000°C. The intense heat of the arc causes the carbon in the coke and the silicon in the sand to fuse into silicon carbide. By varying the speed of the heating and cooling cycle the final crystal size is determined. A long, slow cooling cycle allows a few crystals to grow to a very large size while quick cooling forms numerous small crystals. The cooled mass is then broken up and rough graded by screening. The individual crystals are treated by impact, crushing or air blasting to remove brittle edges. Finally, it is graded by screening, water sedimentation, hydraulic flotation or air classification, with the latter used for the very fine grades.

Because of its extreme hardness, silicon carbide is ideal for grinding Pyrex, which is harder than ordinary glass, or very deep curve generation used for refractor, Maksutov, or richest field objectives. The very coarse sizes (40 and 60) are used for diameters larger than six inches or deep curves where a large amount of glass must be removed.

India Astronomy Club - IAC silicon carbide is the very best optical grade available. Every step during the manufacture and packaging is controlled to ensure the high purity and scratch free qualities sought by the precision optical worker. Accurately graded sizes from 40 to 500 grit are stocked. We recommend this abrasive for use on Pyrex up to the final critical lapping stages

Aluminum Oxide

Slower cutting, ideal for softer flint, crown and low-expansion optical glasses.

Aluminum Oxide is slower cutting, ideal for softer flint, crown and low-expansion optical glasses. In its naturally occurring crystalline state, aluminum oxide, or corundum has been used as an abrasive for thousands of years. The purest, natural form is the gem-white sapphire. Blue sapphires and rubies are also composed of aluminum oxide but have been colored by mineral oxides. Emery, another common natural abrasive, is impure corundum containing iron oxides. The naturally occurring abrasives of this family were subject to large variations in quality. Occasionally, a very fine pocket of aluminum oxide would be mined and provide the optician with exceptional finishes, but more commonly, quality was very uneven and the material had to be cleaned and separated by the difficult, time consuming water flotation process. As you read some of the older books on telescope making you will understand how serious the quality control problems were, and the great pains taken to purify abrasives.

Today, modern technology is capable of producing consistently high quality aluminum oxide which has practically replaced the natural forms for precision optical work. Aluminum oxide, like silicon carbide, is made in the electric furnace. Bauxite (aluminum ore), coke and powered iron are combined, heated, cooled, crushed, treated to produce a uniformly shaped particle and finally graded. This results in a nearly pure aluminum oxide crystal with a hardness of 9 on a Mohs scale. It is somewhat slower cutting than silicon carbide and is therefore ideally suited for smoothing operations involving the softer optical glasses used for refractors, corrector plates and optical windows.

White Aluminum Oxide Lapping Powder

Super fine, smooth cutting, scratch free final stage abrasives.

Final lapping is the key to smooth, regular surfaces that polish out quickly with no turned edges. The professional optician knows that a very fine, closely controlled abrasive makes it possible to grind out in a few minutes slight irregularities which would take hours of polishing to correct. But, when this stage is reached, it is absolutely key to have an abrasive that does not scratch. To meet this need a special white aluminum oxide lapping powder has been developed. Because the ore for this product is nearly pure, no additives in the form of coke or iron are needed as flux which significantly lowers the risk of contamination. The intense heat of the electric arc fuses the white aluminum ore and then by controlling the rate of cooling the very small individual crystals are grown to a uniform size, edge and hardness. The result is a pure white discus shaped particle that cuts by a planning action rather than the fracture method of the more common grey aluminum oxides. We recommend a 12 and 5 micron sequence after 500 grit and before polishing. Usually 3 or 4 wets are needed for each mirror, therefore one quarter pound will last all but the most active worker average long time.

Optical Grade Polishing Compounds

Throughout the grinding and final lapping stages, the objective has been to reduce pits and scratches to the smallest possible size. However, no amount of grinding can produce a surface smooth enough or sufficiently transparent to meet the needs of a first-class telescope objective. Different techniques are needed. While there is still considerable discussion on the subject, it appears that polishing is a result of one or more of the following: removal / wear, athermic surface flow, or the formation of a silica-gel surface by hydrolysis. The result, whatever the cause, is an incredibly smooth surface, if proper techniques and optical grade supplies are used.

Until recently there were three principle types of optical polishing compounds available; Barnesite, cerium oxide, and the iron oxides (or more commonly, rouge). Barnesite production was severely restricted when the manufacturer determined that the process could not meet federal anti-pollution controls. Fortunately, cerium oxide and the various rouges are more than sufficient to meet the needs of the precision lens maker.

All of our polishing compounds will give a first-class polish, but each one differs from the other in speed, action, cleanliness and cost. By changing from one to another during the polishing and figuring stages, it is possible to finish a mirror or lens faster and more accurately because the primary difference is speed. Therefore you may want to polish out your surface rapidly with cerium oxide and then switch to one of the slower acting rouges that allow you literally to creep up to the exact figure you are working for without fear of overshooting.

Zirconium Oxide

Slow, clean, scratch and sleek-free polishing. Zircon is a fairly soft, ductile, gray or black metallic chemical element which is used in alloys and ceramics. The zirconium oxide we sell is white and very slow acting. Ideal for final figuring.

Red Rouge

Low cost, time-proven high quality polishing.

Red rouge is produced by combining ferrous sulfate, ammonium hydroxide and ammonia water. The solution is then filtered, burned in the presence of air and finally powered and graded. Its close cousin is iron rust, although optical rouge is many times finer and purer. Generations of skilled craftsmen have used rouge to produce surfaces of the highest quality.

Our red rouge is soft, slow polishing, and leaves no sleeks. It gives the polishing lap a smooth, velvety feel. Care is needed in its use since it does not readily wash out of clothes. Ideal for the final 8 to 10 minutes of figuring when fast changes can cause you to overshoot the desired curve.

Optical Grade Rosin, Pitch and wax

The polishing stage of mirror making accomplishes two things. First, it smooth's the surface so that light can pass through or be reflected without scattering to form a clear, sharp image. Second, the surface is then changed (or “figured”) to match an ideal curve to further sharpen the image. These two steps produce surfaces that do not deviate by more than 1/4 to 1/20 wavelength of light or one-two hundred thousandth to a millionth of an inch. To achieve this high degree of precision, pitch, wax and rosin are used to form a polishing lap that behaves like a very thick liquid and slowly flows and conforms to the mirror’s surface. The very highest quality astronomical surfaces are made on pitch laps. While laps of paper, plastic and felt have been used, none have proven to be a match for the pitch lap.

Rosin

Ideal for tempering laps.

Rosin is a solid resinous material that occurs naturally in the oleo resin of the pine tree. Commercially, pine trees are tapped for their sap or gum. The collected gum is thinned with turpentine and a small amount of oxalic acid is added to remove the trace of iron that southern pine trees absorb from the red soils. This solution is then steam heated to between 180 and 200°C., filtered and washed with water to remove the remaining oxalic acid and other soluble acids. Finally, high pressure steam is used to drive off the turpentine, and the liquid is cooled into a solid. The rosin mass does not flow like pitch but rather remains stable over a reasonably wide temperature range. The highest quality rosin is amber colored and is transparent. Rosin is soluble in most organic solvents — turpentine or ethyl alcohol. It is a valuable additive to pitch (where it acts to temper the pitch so that it flows more predictably and evenly) as an ingredient in blocking pitches, or as a lap in very high temperature zones.

Pitch

The key to outstanding surfaces.

India Astronomy Club IAC pitch, like rosin, begins with the gum from a pine tree. However, unlike rosin, pitch is produced by heating the gum in the absence of air. As the temperature increases the very volatile elements, then light through heavy oils, boil off, until only cyclic organic acids or pine-tar pitch remains. It is cleaned and processed until it is a clear burgundy colored homogeneous mass. Pitch is soluble in organic solvents.

India Astronomy Club IAC offers pure pitch in soft grade and in a special tempered, ready to use formula. The pure pitches can be used alone or as a base to which rosin, beeswax and linseed oil can be added.

For the beginner or advanced worker who does not want to mix his own pitch we offer tempered burgundy pitch, a unique combination of rosin, beeswax and pitch that melts at 174°F, flows accurately for normal focal length mirrors and flats and is consistent from package to package and year after year. This pitch is the favorite of thousands of ATMs and professionals.

Refined beeswax

Ideal for tempering laps, as a top coating to laps and a low melt blocking wax.

To store honey, the honey bee builds a comb with wax produced in his body. To retrieve the wax, empty combs are melted in boiling water, and the wax floats to the top and is skimmed off. The non-optical grade beeswax is not usually further processed. The optical grades are refined to remove color, residual honey and grit. The result is a clean, creamy white product.

If 5 to 10% beeswax is added to pitch, it reduces chipping when channels are cut in the lap. Further, the addition of beeswax tends to temper the lap making flow more predictable. Many workers apply a thin, pure coat of beeswax over the squares in a channeled lap to ease binding of the mirror and to stop sleeks. It can also be used as a low melting point blocking wax that softens with hot water.

To buy above mentioned things,check the link below. One stop shop for all amateur telescope making materials. 

https://sites.google.com/view/india-astronomy-club-iac/shoppping/telescope-making