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Subject: Casting techniques for wooden carving

Casting techniques for wooden carving

From: Gene McCall <gmccall>
Date: Saturday, April 29, 2006
Frank Hassard <f.hassard [at] tiscali__co__uk> writes

>I am working on a reproduction Chippendale cabriole leg chair
>(c.1860) carved in mahogany. One of the ear-pieces to the top of the
>proper right side is missing. ...
>...
>... I think it may be possible to cast a new one from one of the
>existing ear-pieces (and then tailor it to suit). However, I do not
>have much experience with such techniques. I understand that there
>are concerns with some of the epoxy systems regarding
>discolouration, texture etc. Could someone give me some advice on
>how to get the best results and which materials/techniques are
>presently favoured (and ethically acceptable)? ...

Reading some of the responses to this inquiry made me think that no
matter how well intentioned the advice was intended to be, much of
it was simply barking up the wrong tree.

The "ear-piece in question will rarely, if ever, be exactly
identical to its counterparts because they were generally carved by
hand with the aid of little more than a ruler and pencil.  If the
chair is not part of a set, the other "ear-pieces" will also
generally have different angles or else be a mirror image of the
missing piece.  Also, on a Chippendale chair (reproduction or
otherwise) the "ear-pieces" rarely exhibit daunting complexity or
extreme undercuts.  Breaking the job down into a series of logical
steps can often make it more manageable.

By observing the underside of the rail where the original piece was
attached one can usually observe the exact outline of the original.
This will establish the correct exact length of the missing piece.
The exact angle formed by the two flat faces that form the glue
surfaces of the chair leg and adjoining rail can be easily
established with an adjustable square, or even a pencil and piece of
cardboard for that matter.  The curve of the outer face of the leg
where the missing piece was formerly attached will establish the
exact convex profile of the missing piece, as well as the exact
locations and depth of the carved details.  Looking at the other
"ear-pieces", and even tracing from them if needed, will establish
many of the other details of the carved decoration.

If you first cut the wood block which will become the "ear-piece"
(with the grain running in the correct direction and a bit thicker
than required) to match the angle of the existing glue faces you can
be assured of a perfect fit.  Then it is a simple matter to place
the block in its correct final position and trace the exact curved
profile of the carved face.  Leaving about 1/8 inch of extra wood
for the carving, either band-saw or belt-sand away the waste portion
of the block.  Now you are ready to draw the carving exactly where
it belongs so that it perfectly matches the existing carving on the
leg as well as the angle established by the rail.

At this point you have already done the most difficult part of the
job and the actual amount of "carving" required is minimal. If you
are still uncomfortable with your ability to carve the ear, model it
in clay or plastilina first using wax paper as a barrier so that the
plastilina never comes in direct contact with the original surface
of the chair.  But really, this probably won't be necessary because
most of your work on the wood block is established in advance with a
pencil.  If you draw it correctly first, you will carve it
correctly, because it really is simple at that point.

If you are concerned that your work might be mistaken as original
during some future examination, don't be.  Use a different finishing
material than the original or a different type of stain, and the
added piece will be clearly distinguishable under ultraviolet light
or other examination techniques in the future.

There is really no need to utilize a sub-millimetre 3-D laser
scanner, a computer numerically controlled CNC machine, rapid
prototyping technologies, or even to subject the original surface of
the chair to chemicals or barrier creams while utilizing tried and
true casting methods.  I am not criticizing the use of these
technologies.  All of these techniques have their proper uses in
conservation, but in this case I feel it would be like shooting a
mosquito with an elephant gun.

Your goal of conserving this chair will be accomplished less
intrusively, more faithfully, and without ethical compromise, if you
just use a sharp pencil, sharp chisels, common woodworking tools and
some faith in your ability to learn a new skill if you just take it
one step at a time.

Incidentally, the project you describe is just the kind of thing I
like to let an apprentice sink his or her teeth into, because it can
be a valuable learning experience without the risk of causing damage
to an original piece of cultural property.

Gene McCall
President
Gene McCall Conservation and Restoration Inc.
860-D South River Road
Englewood, Florida 34223
941-473-1348
Fax: 941-473-2444


                                  ***
                  Conservation DistList Instance 19:53
                  Distributed: Sunday, April 30, 2006
                       Message Id: cdl-19-53-002
                                  ***
Received on Saturday, 29 April, 2006

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