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Subject: Displaying iron cannon

Displaying iron cannon

From: Paul Harrison <pharrison>
Date: Friday, September 27, 2002
Jason M. Burns <oldcitymaritime [at] yahoo__com> writes

>What is the preferred method of displaying iron cannon outdoors
>today?  I have been asked to look at a few cannons here locally
>displayed.  Concrete plugs installed in the barrels of two 18th
>Century iron cannons are obviously not working and allowing water to
>get into the barrels.  What materials are being used to seal the
>barrels for display?

I'm responsible for about sixty cannons on display and in store in
Hong Kong both in public places and museums.

I did contact some museums in the UK and got from one a good, but
fairly complicated, design that involved a circular disc with a
screw threaded bar that meets the disc perpendicularly on the screw
thread is a disc. If you imagine that the disc is like a table top,
it then had 4 triangular legs. So by tightening the screw from the
outside, the inside disc pushes on the hypotenuse of the triangle of
the 4 legs, this pushes the legs out and this grabs the inside of
the barrel. I have only made a demonstration model out of card of
this method.

I usually cut 2 thick perspex/plexiglass discs (tompions) to fit in
the cannon about 2 inches inside the barrel, I paint both sides
black, as most of my cannons are painted black (CF Henry Ford and
the Rolling Stones.) Doing this means if a tompion is scratched, it
is still black. I put in the barrel a textile sausage containing
blue silica gel, this often snags on rust on the way in, so I
surround the sausage in Melinex, polyester film, and push the
sausage and film in, I then pull the Melinex out.

The tompions are then stuck in, I apply two as a failsafe, and
attach them in place with rapid setting epoxy adhesive, coloured
black with epoxy adhesive pigment, (Araldite).  The amount of the
circumference that I stick is proportional to the situation where
the cannon will be displayed, I do epoxy the base as there will
sometimes be a small puddle of water collected there. To fill the
remaining  gaps, I seal the gap with black silicon rubber.

I have thought of but not yet tried putting in between the two
tompions, one plastic bag inside another bag and filling it with
expanding polyurethane foam. This would give further protection to
the inside from vandals and the elements.

This system seems to be effective, in that the inside of gun barrels
are difficult to remove corrosion from and so by putting in the
silica gel, it helps keep it dry and inactive. The tompion is inside
the barrel, and so is not too intrusive, if the barrel were to de
displayed at an angle, I would have the tompion closer to the mouth
to stop rainwater collecting in a puddle there.  Many tompions are
right at the muzzle of the gun and may interfere with the proper
appreciation of it.

It also 'buries' blue silica gel, that is a health concern about. I
have only ever had to do minor repairs to two tompions so far, (they
were done by the prototype of this method)

Paul Harrison
Metal Conservator
Hong Kong Govt.

                  Conservation DistList Instance 16:25
                Distributed: Wednesday, October 2, 2002
                       Message Id: cdl-16-25-001
Received on Friday, 27 September, 2002

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