The Chelsea Filter
compiled by Cheryl Castner
The Chelsea Filter is a tool that helps confirm what something is NOT. It can not identify what something is. Use it with reservation, as all reactions should be confirmed with other more reliable gem identification instruments.
| Stone | Reaction |
| Green Stones | |
| Alexandrite | Red |
| Aquamarine | Distinctly Green |
| Aventurine Quartz | Reddish |
| Chrome Chalcedony | Red |
| Chrysoprase | Green |
| Demantoid Garnet | Reddish |
| Emerald (some Emeralds from South Africa and India may not show a Red hue, but remain Greenish) | Pink to Red |
| Enstatite | Green |
| Fluorite | Reddish |
| Glass (Paste) | Green |
| Hiddenite | Slight Pink |
| Jadeite | Green |
| Peridot | Green (Aqua Blue) |
| Sapphire | Green |
| Soude Emerald (the old type Soude emerald may show red) | Green |
| Stained Bowenite | Red |
| Stained Chalcedony | Red |
| Stained Jadeite | Red |
| Synthetic corundum (alexandrite effect) | Red |
| Synthetic emerald | Strong Red |
| Synthetic Sapphire | Red |
| Synthetic Spinel (some old types may show green) | Red |
| Tourmaline (Certain anomalous green tourmalines have been found to show Red – which would indicate chrome tourmaline) | Green |
| Tsavorite Ganet | Red |
| Uvarovite Garnet | Pink |
| Zircon | Reddish |
| Red Stones | |
| Garnets, dark red, no fluorescence | Red |
| Garnet topped doublet , no fluorescence | Dark Red |
| Glass, paste, no fluorescence | Reddish |
| Ruby, natural and synthetic, strong fluorescence The natural and synthetic sapphire are indistinguishable under the color filter) | Red |
| Spinel, fluorescent | Red |
| Spinel, synthetic, fluorescent ( pink synthetic spinel does not show a red color through the filter) | Red |
| Blue Stones | |
| Aquamarine | Distinctive Green |
| Garnet topped doublet | Greenish-blue |
| Glass, paste, dark blue | Red |
| Glass, paste, light blue | Greenish |
| Lapis lazuli | Weak brownish red |
| Sapphire, blackish (The Blue sapphire which shows a Purple color under artificial light, usually shows Red under the filter) | Green |
| Sodalite | Slightly brownish |
| Spinel | Reddish |
| Spinel, colored by cobalt | Red |
| Swiss lapis, greenish-blue | Greenish blue |
| Synthetic sapphire (The natural and synthetic sapphire are indistinguishable under the color filter) | Dark Greenish Blue |
| Synthetic Spinel,dark blue | Red |
| Synthetic Spinel, light blue | Orange |
| Synthetic Spinel, zircon color | Orange to Red |
| Synthetic Spinel, lapis lazuli color | Bright Red |
| Zircon | Greenish |
| Purple Stones | |
| Amethyst | Reddish |
| Violet Sapphire | Bright Red |