On Making Intarsias"
By Meredith Jones
Kitsap Mineral and Gem Society
There are many details in this lapping process to be
explained. I use a ¾-inch sheet of plywood for a turntable about
2½ feet in diameter. My intarsias are secured with wood screws through
the plywood turntable and turned at about 250 r.p.m. with a ½ h.p.
motor. The intarsia, being rectangular, should have temporary extension
pieces added to the sides to allow lapping to the far corners. See Fig.5.
The top pieces being lapped are held and controlled
by a hinged arm of pipe or rod mounted on a pivot above and across the turntable.
To each slab that is used as a lapping tool, bond a small section of ¾-inch
plywood containing a 3/8-inch hole in its center. The hole will receive
the pivot point on the cross arm and when the bottom lap revolves this top
piece will also turn. Add grit and water as he cross arm is moved from side
to side and the resulting grinding action is really terrific. Use downward
pressure and continue applying grit and water until both pieces are lapped
smooth and flat.
Starting frit on most intarsias should not be courser
than 220 as soft areas quickly eat away with course grit and leave hollow
areas. From 220 progress to 500 and then 1200 grit.
Polishing is very simple. A very high luster can be
obtained by using a flat wad made of a wool rug n the same manner. Apply
any good polishing agent such as tin or cerium oxide with water. I use red
iron oxide (rouge) because it also polishes well and is very cheap but,
unfortunately, also very dirty. It can stain some porous materials.
The polishing operation normally runs at least an hour
or two, although some material develops a high luster in ten minutes. Continuous
attention is not necessary if the cross arm is secured in a fixed position
and properly weighted. Check and keep the polishing pad moist by adding
water at least every half hour until satisfied with the polish. The rug
pad can cover the turntable with the work in the top position if the piece
to be polished does not overhang the turntable.
This may be confusing but I hope Fig. 5 will give a
better picture of what I call upside down lapping.
The lapping method can be used on practically l flat
surfaces and some suggestions are in order. Small flat pieces can be laid
face down on a sheet of glass and plaster poured over them to form a slab,
which can then be lapped and polished
walnut table inset with petrified wood log sections and buffaloes made of
patrified wood. White plastic forms rthe oval. The entire top is finished
in clear plastic. A matching chest has the same design on both top and front.
The log section is made from a wedge-shaped piece of petrified wood, cut
into nine slices, and fitted to gether to form the finished circular slab.
Made by Meredith Jones.
Before writing this article I was asked to describe
the methods I use which, no doubt, are not the same as those used by a lot
of people. The thought behind the effort can be summed up by a recent remark
of a friend, 'If I give you a dollar and you give me a dollar, we will both
still have one dollar, but if I give you an idea and you give me an idea,
we have both profited because now we have two ideas.' My hope is this article
will make many fellow gem cutters just a little richer."