Gemstone Cutting, Grinding and Polishing

Gemstones are natural or synthetic minerals with special physical properties that may be fashioned into objects for personal adornment and decorative purposes. To cater to the increasing demand for gemstones, the Gemstone Cutting, Grinding and Polishing Processes are being utilized.

Materials: Various types of gemstone such as Jade, Opal, Quartz, Chert petrified wood, Jasper and/or other semiprecious stones.

Consumable Needed:

  • Diamond cutter blade Chromite oxide
  • Dopping stick Grinding wheel, 80/120 grits
  • Template Shellac flakes/epoxy
  • Pencil Alcohol lamp
  • Sand paper, 200/600 grits Denatured alcohol
  • Polishing cloth/carpet Tweezers

Equipment Needed:

  • Gemstone Cutting Machine
  • Gemstone Grinding Machine
  • Gemstone Polishing Machine

Procedure:

  1. Orientation/Examination of Samples. Carefully examine the raw stone to avoid cracks, fractures and cleavages to get the best part of the stone.
  2. Slabbing. Cut the rough stone into 3-5 mm slices or 4-6 mm thick using the cutting equipment. This can be done in 5 minutes.
  3. Templating. Outline the desired cabochon shapes on the slabs using a template and aluminum pencil. The outline serves as a guide for trimming and grinding.
  4. Trimming. Remove the unnecessary part in the slabs following the outlined shapes. Maintain 1.5-2.5 mm space around the outline for grinding purposes. This can be done within 3 minutes.
  5. Preforming. Do initial grinding by following the contour of the desired shape by using the grinding machine. The marked piece, held firmly in both hands, is applied to the wheel face at about the level of the axle and ground to about 1/32 of an inch of the template outline.
  6. Dopping. This is done by attaching the flat side of the stone to a dipstick with a heatsealing wax mixture. Dopstick may be bought or improvised using a rod that is 18-21 cm long and 2 cm in diameter. The stone is heated and pressed against the waxed end of the dopstick.
  7. Shaping (Grinding). Final grinding is done in an 80-120 grits grinding wheel in order to attain the desired shape and size.
  8. Sanding. Sanding is done to prepare the ground gemstone for polishing. Sand papers of grits of 220 and 600 are used in this process. Sanding may be done in 3 minutes.
  9. Polishing. Rub the gemstone against a soft material such as felt, leather, cloth or carpet
    on which a watery polishing agent is applied to impart a glossy smooth surface.
  10. Unmounting from Dopstick. Remove the polished gem from dopstick by picking it with a cutter or any pointed material.

Note:

All the above-mentioned processes except 1, 6 and 10 require water to avoid burns on the surfaces of the stone. In order to ensure cleanliness, workpiece should be washed before changing cutting media (diamond blade, grinding wheel, polishing compound, sandpapers), since contaminants from previous cutting media would leave deep marks/scratches.

For more information, contact:

Metals Industry Research and Development Center (MIRDC)
MIRDC Compound Gen. Santos Ave.
Bicutan, Taguig, Metro Manila
Tel. No. 837-04-31 to 38
Fax No. 837-04-30
www.mirdc.dost.gov.ph

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