Conservation Science

(red rust)

(16)

(magnetite)

(17)

Chloride-based iron compounds either sublime at the operating temperatures
or reduced in the presence of hydrogen to form hydrogen chloride. A typical
reaction would be

(18)

This magnetite/iron mixture is very friable and must be consolidated imme-
diately if the shape of the artefact is to be maintained. The large guns recovered
from the Solent were placed in tanks of low-viscosity epoxy or polyester resin
where impregnation occurred. Figure 13 shows two similar guns from HMS
Pomone, one before, and the other after, treatment in the hydrogen furnace.

FeCl 22 H →Fe 2 HCl

Fe O 23  323 H 2 → Fe H O 2

Fe O 23 →Fe O 34

Metals 157

Figure 13Similar caronades from HMS Pomone before and after conservation in the
hydrogen furnace