Merle's Surprise
Cut
Concave
facet design
by
Chris Algar
 
Beginner-to-intermediate
Chris Algar offers “An Introduction to Concave Faceting” on page
30 of the August 2003 Lapidary Journal Jewelry Artist.
When I proposed an article on concave faceting to Lapidary Journal editor Merle
White, she asked if I'd add a Step by Step project to go with it. So I surprised
her with this!
This straightforward design should present little difficulty because it’s
basically a step cut with no spiral facets. The size of the facets relative to
each other is a choice to be made by individual cutters — the drawings can
be used as a guide. The depth of the concave facets, most noticeably those around
the girdle, will be determined by the diameter of the lap compared to the size
of the stone. |
Faceting Instructions |
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technical
data |
| • A hexagonal, cut corner stone
with the table as the only flat facet
• 96 index gear
• Angles for cubic zirconia
• 19mm (0.75") diameter cylindrical lap
• Finished stone — 13.2mm |
For information on supplies, please see the Annual
Buyers' Directory.
Always ask for the MSDS (Material Safety Data Sheet) for any materials you buy,
which will give you reactivity, health hazard, and safe handling data.
|
| 
|  Chris
Algar lives near Heathrow airport, England, with his wife, four cats, and an unknown
number of amphibians. The couple became interested in lapidary during visits to
the United States, where they enjoyed the bright weather and low population of
the desert Southwest. They have spent many happy hours photographing insects and
rockhounding with their American friend, Judy Murphy. The only facetable material
they have collected is Oregon sunstone.
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|
 |
| Pre-formed stone |
Pavilion
Preform with flat facets at:
| Step |
Angle |
Index |
| 1 |
41° |
8-24-40-56-72-88 |
| 2 |
90° |
96-16-32-48-64-80 |
| 3 |
90° |
8-24-40-56-72-88 |
| Cut off corners.
Transfer to concave faceting machine. |
|
|
|
| Pre-formed stone |
Completed tier of facets |
 |
| First concave girdle facets in place. |
| Step |
Angle |
Index |
| 4 |
41° |
8-24-40-56-72-88 |
| 5 |
90° |
96-16-32-48-64-80 |
| Step |
Angle |
Index |
| 6 |
90° |
8-24-40-56-72-88 |
 |
| All girdle facets now cut. |
| Step |
Angle |
Index |
| 7 |
46° |
8-24-40-56-72-88 |
 |
| Cut next facets half way to culet. |
| Step |
Angle |
Index |
| 8 |
58° |
96-16-32-48-64-80 |
 |
| Level girdle. |
| Step |
Angle |
Index |
| 9 |
51° |
96-16-32-48-64-80 |
| |
| Use this step and the next to set relative facet sizes. |
| Step |
Angle |
Index |
| 10 |
43° |
96-16-32-48-64-80 |
Polish all facets including those around the girdle.
Transfer the stone. Align the stone at index 96 by loosening the quill and
then resting the stone on a stationary flat polishing lap. As the girdle facets
have already been cut and meet points established, flat preforming is optional
on the crown. It is, however, a good way of removing excess material. If you decide
to take the preform route, leave plenty of girdle thickness into which the concave
facets can be cut. |
|
 Crown
Preform flat facets at:
| Step |
Angle |
Index |
| 1 |
48° |
96-16-32-48-64-80 |
| 2 |
48° |
8-24-40-56-72-88 |
| Crown preformed with flat facets.
Transfer to concave faceting machine. |
| Step |
Angle |
Index |
| 3 |
48° |
96-16-32-48-64-80 |
| 4 |
48° |
8-24-40-56-72-88 |
| Crown preformed with flat facets.
Transfer to concave faceting machine. |
This diagram shows a concave facet (red) being cut into a preformed flat facet.
If the concave facet is being cut correctly, the remaining parts of the flat facet
(on either side of the concave facet) will be mirror images of each other. Unevenness
should be corrected by adjusting the stop against which the dop rests. Alignment
should be accomplished by the time the concave facet reaches the girdle and the
flat facet has been cut away.
The first tier of concave facets on the crown has been completed. |
|
| Step |
Angle |
Index |
| 5 |
38° |
96-16-32-48-64-80 |
| 6 |
48° |
8-24-40-56-72-88 |
| The second tier has been added. |
| Step |
Angle |
Index |
| 7 |
28° |
96-16-32-48-64-80 |
Cut these facets so that they meet the points formed by Step 6.
Polish all facets. Return to the flat faceting machine and cut and polish the
table. Alternatively, cut the table and then return to the concave machine to
polish the other facets.
Table has been added.
|
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