Polish cut gemstones to final finish via progressive abrasive sequences. Pre-polish sanding, polishing compounds, lap pick, quality assess for cabs + faceted. Use → cab/faceted post-cut ready for polish, pick compound + lap for species, troubleshoot failed polish (orange peel, haze, scratches), re-polish worn stone.
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Polish cut gemstones to final finish via progressive abrasive sequences. Pre-polish sanding, polishing compounds, lap pick, quality assess for cabs + faceted. Use → cab/faceted post-cut ready for polish, pick compound + lap for species, troubleshoot failed polish (orange peel, haze, scratches), re-polish worn stone.
Pre-Polish Surface Check:
+--------------------+------------------------------------------+
| Check | Requirement |
+--------------------+------------------------------------------+
| Previous grit | All scratches from the cutting stage |
| scratches | must be removed by the final grit |
| | (typically 1200 or 3000) |
+--------------------+------------------------------------------+
| Surface uniformity | No flat spots on cabochons, no uneven |
| | facets on faceted stones |
+--------------------+------------------------------------------+
| Cleanliness | Stone thoroughly cleaned between grits |
| | and before polishing. Grit contamination |
| | is the #1 cause of polish failure |
+--------------------+------------------------------------------+
| Dop security | Stone securely dopped — shifting during |
| | polish destroys facet geometry |
+--------------------+------------------------------------------+
Examine under 10x mag
Look for cutting-grit scratches → parallel lines
Scratches remain → return to appropriate grit before polish
Clean thoroughly: ultrasonic or brush w/ dish soap + water
Clean hands, dop, work area → grit contamination transfers easily
→ Scratch-free surface at pre-polish grit, thoroughly cleaned, secure dopping. Glass-smooth to fingernail.
Cabochon Pre-Polish Sequence:
+------+-----------+------------------------------------------+
| Stage| Grit | Purpose |
+------+-----------+------------------------------------------+
| 1 | 220 | Shape and dome (cutting stage — done) |
+------+-----------+------------------------------------------+
| 2 | 600 | Remove 220 scratches, refine shape |
+------+-----------+------------------------------------------+
| 3 | 1200 | Remove 600 scratches, smooth surface |
+------+-----------+------------------------------------------+
| 4 | 3000 | Remove 1200 scratches (optional but |
| | (or 1500) | recommended for hard stones like agate) |
+------+-----------+------------------------------------------+
| 5 | 8000 | Pre-polish (some machines include this) |
| | (or 14000)| Fine diamond paste on appropriate pad |
+------+-----------+------------------------------------------+
TIME PER GRIT: Spend equal time at each stage. Rushing a grit
stage means scratches carry forward and become visible after
polishing. A typical cabochon takes 3-5 minutes per grit stage.
Each grit in order — never skip
Per stage, examine under mag → confirm prev-grit scratches gone before advance
Clean stone + hands between grits
Consistent pressure + motion across surface
Water flowing → prevent heat buildup
→ Uniform satin-smooth surface, no scratches under 10x mag.
If err: scratches persist at grit → continue, don't advance. Deep scratches won't come out → drop back one grit, re-grind. Coarser-grit contamination = top cause of persistent scratching.
Step 3: Compound + Lap Selection
Pick correct compound + lap per species.
Polishing Compound Guide:
+-------------------+------------------------------------------+
| Compound | Best For |
+-------------------+------------------------------------------+
| Cerium oxide | Quartz family (agate, jasper, amethyst, |
| | chalcedony), feldspar, obsidian |
| | Mix: paste consistency with water |
| | Lap/pad: leather, felt, or Batt |
+-------------------+------------------------------------------+
| Diamond paste | Universal — works on everything |
| (50,000 mesh / | Essential for corundum, spinel, topaz, |
| 0.25-0.5 micron) | garnet, and other hard stones |
| | Lap: tin, copper, ceramic, Corian |
+-------------------+------------------------------------------+
| Aluminum oxide | Corundum (ruby, sapphire), spinel, |
| (0.3 micron) | chrysoberyl |
| | Lap: ceramic, tin, wax |
+-------------------+------------------------------------------+
| Tin oxide | Quartz varieties, opal (gentle polish) |
| | Lap: leather, felt, Lucite |
+-------------------+------------------------------------------+
| Chromium oxide | Jade (jadeite, nephrite), emerald |
| (green compound) | Lap: leather |
+-------------------+------------------------------------------+
| Linde A | Corundum, spinel — traditional choice |
| (aluminum oxide) | Lap: wax, ceramic, tin |
+-------------------+------------------------------------------+
Polishing Lap Guide (Faceted Stones):
+-------------------+------------------------------------------+
| Lap Material | Use |
+-------------------+------------------------------------------+
| Tin (type metal) | General-purpose polish lap. Good for |
| | most stones with diamond or alumina |
+-------------------+------------------------------------------+
| Copper | Diamond polish for hard stones |
| | (corundum, spinel, topaz) |
+-------------------+------------------------------------------+
| Ceramic (BATT, | Diamond polish. Forgiving, good for |
| Darkside, Last | beginners. Works on most materials |
| Lap) | |
+-------------------+------------------------------------------+
| Corian (solid | Oxide polishes. Good for quartz family |
| surface) | |
+-------------------+------------------------------------------+
| Lucite/Plexiglass | Oxide polish for quartz, softer stones |
+-------------------+------------------------------------------+
| Leather/felt | Cabochon polishing. Cerium oxide or |
| | tin oxide |
+-------------------+------------------------------------------+
Match compound to species
Pick lap/pad material
Unknown/uncommon stones → diamond paste on ceramic = safest start
Prep compound: oxides → thin paste w/ water; diamond paste sparingly on lap
Apply evenly → excess = "orange peel" texture
→ Compound + lap combo appropriate for species. Wrong combo = wasted time, sub-optimal finish.
If err: standard compound doesn't polish well first try → (1) different lap material, (2) finer compound grade, (3) reduce pressure. Polishing-speed-sensitive stones → slower rpm. All else fails → diamond paste on tin or ceramic works on virtually anything.
Step 4: Final Polishing
Execute polish.
Polishing Technique:
CABOCHON POLISHING:
1. Apply compound to the leather/felt wheel
2. Run the wheel at moderate speed (lower than grinding)
3. Hold the stone lightly — REDUCE pressure compared to grinding
4. Move the stone across the wheel surface with gentle sweeping motion
5. Polish for 2-5 minutes, checking progress with a loupe
6. Add compound sparingly — too much creates orange peel
FACETED STONE POLISHING:
1. Charge the polishing lap with compound
2. Set the SAME angle as the cutting stage for each facet tier
3. Lower the stone gently onto the spinning lap
4. Polish each facet with light, consistent pressure
5. Check each facet under a loupe before moving to the next
6. Re-charge the lap periodically but do not over-charge
SPEED AND PRESSURE:
- Polishing speed: 50-75% of cutting speed
- Pressure: LIGHT — let the compound do the work
- Heavy pressure causes heat, orange peel, and facet rounding
- On faceted stones, heavy pressure rounds facet edges ("soft meets")
Apply compound to lap/pad
Set correct angle (faceted) or hold dome angle (cab)
Polish w/ light, even pressure
Check progress every 1-2 min under 10x
Continue until full lustre, no remaining scratches
Final rinse → remove all compound residue
→ Fully polished surface w/ mirror lustre (faceted) or deep even lustre (cab). No scratches under 10x. Sharp facet edges + crisp meets.
If err: common polish problems + solutions:
Orange peel (textured): Too much compound, pressure, or contaminated lap. Clean lap + re-apply sparingly
Soft meets (rounded facet edges): Too much pressure. Reduce + use harder lap
Haze (no full lustre): Wrong compound for material, or compound too dry. Different compound or add water/extender
Step 5: Quality Assessment
Inspect under mag.
Final Quality Checklist:
+--------------------+------------------------------------------+
| Criterion | Standard |
+--------------------+------------------------------------------+
| Lustre | Full, even lustre across all surfaces |
| | No dull patches or haze |
+--------------------+------------------------------------------+
| Scratches | None visible under 10x magnification |
| | Check under multiple light angles |
+--------------------+------------------------------------------+
| Orange peel | None — surface should be optically flat |
| | on each facet / smoothly curved on cabs |
+--------------------+------------------------------------------+
| Facet edges | Sharp and well-defined (faceted stones) |
| (faceted) | No rounding or "soft meets" |
+--------------------+------------------------------------------+
| Dome uniformity | Smooth, even curvature (cabochons) |
| (cabochons) | No flat spots or high points |
+--------------------+------------------------------------------+
| Cleanliness | All compound residue removed |
| | Stone cleaned ultrasonically or by hand |
+--------------------+------------------------------------------+
Clean thoroughly → residue can mimic polish
Examine under bright directional light at multiple angles
10x mag → check remaining scratches
Faceted: each facet individually + verify meet precision
Cabs: dome reflects single undistorted light point ("light return test")
Record final weight + dimensions
→ Pro-quality polish: full lustre, no scratches under 10x, sharp facet edges or smooth dome, clean of residue. Ready for setting, display, sale.
If err: specific areas fail → spot-polish individual facets (faceted) or return to wheel for areas (cabs). Don't re-polish whole stone unless defect widespread.
Check
Pre-polish surface scratch-free before polishing
Stone + equipment cleaned between every grit
Correct compound selected for species
Appropriate lap/pad used
Light pressure throughout
No scratches under 10x in final inspection
Full lustre across surfaces
Facet edges sharp (faceted) or dome smooth (cab)
All residue removed in final cleaning
Traps
Grit contamination: #1 cause of polish failure. Single 220 grain on polishing lap → deep scratches. Clean obsessively between stages.
Too much pressure: Heavy → heat (can crack stone), orange peel, rounded facet edges. Let compound work — pressure barely > stone's weight.
Too much compound: Over-charging lap → slurry layer → orange peel not flat polish. Apply sparingly + re-charge periodically.
Wrong compound for species: Cerium oxide great on quartz, poor on corundum. Diamond paste works on everything but expensive. Match to stone.
Skip inspection: Always check under 10x before declaring complete. Naked-eye-invisible defects → obvious once set in jewellery or examined by buyer.
→
cut-gemstone — cutting must be done properly before polish; scratches from cutting can't be fixed during polish alone
