dk nkf - Nordisk Konservatorforbund Danmark

Figure 3: Disassembled pump components awaiting electrolytic
reduction.
port pump, as it was possible to judge the exact depth
of concretion to remove before reaching the original
surface of the object, and to better understand the
configuration and location of internal components.
Deconcretion and disassembly of the port pump was
accomplished using a variety of hand tools such as
hammer and chisel, scalpels, plastic and hardwood
modeling tools. Pneumatic air-scribes were used to
break up and remove concretion. Flame deconcretion
was also used to remove concreted sediment from
copper alloy and some iron components. [4] During
deconcretion, conservators uncovered manufacturer’s
casting marks on the pump cradle that identified the
maker, model number, and patent number. Although
the preservation of original shape and casting details
was excellent, the surface had become very soft due
to loss of metal. Marine-recovered cast iron loses
much of its strength due to the process known as
graphitization, in which iron in the outer surfaces
is lost to corrosion, leaving behind a soft graphite
matrix. [5] As a result, great care was taken in
handling and cleaning the surface of the pump’s iron
castings (Figure 2).
In many cases the wrought iron fasteners had
completely corroded away, allowing components
such as cover plates to be removed by carefully
separating the plate from the rubber gasket with
a scalpel or long saw blade and removing the
component. In areas where copper alloy fasteners
were used, the preservation of the bolts and
threads was much better, and could be unscrewed
as originally intended using off-the-shelf or
130
custom-made tools padded with rubber, foam or
cloth to prevent damage to the original parts.
Disassembly challenges varied with the design, type
of alloys involved, condition of fasteners, and the
presence and condition of rubber gaskets or sealing
material. Parts which had become firmly adhered to
each other, particularly due to galvanic corrosion at
interfaces between iron and copper alloy components,
were much more difficult to separate. In some
cases, limited pressure was applied using ratcheting
rigging straps to gently pull components apart. The
weakness of the graphitized cast iron was an important
consideration during disassembly. Visible cracks and
loose fragments indicated that there was a limit to
the amount of force which could safely be applied to
loosen and separate components. The disassembly of
mechanical parts is often easy when their condition is
poor and much more difficult when their condition is
good. This paradox must be addressed on a case-bycase
basis when making decisions about disassembly.
Despite these challenges, conservators and technicians
disassembled the pump into 57 component parts that
were individually documented and catalogued prior to
further treatment (Figure 3).
Following disassembly, the port pump components
were placed in an electrolytic reduction (ER)
treatment which, when carefully applied, has been
shown to be very effective in treating marinerecovered
metal artifacts. [6] Electrolytic reduction
serves three functions in the treatment of marine
recovered metals; to reduce corrosion products, to
loosen concretion and sediment, and to increase the
diffusion rate of chloride ions out of the metal. [7]
A 1.0% sodium hydroxide (NaOH) solution in deionized
water at pH 12 was used as the electrolyte, with
an expanded mesh 316 stainless steel anode. Artifact
connections were made by using stainless steel bolts
threaded into original threads in the castings, or by
using undersize bolts through non-threaded holes
secured with stainless steel washers and nuts. A
potential of -0.950 V vs. standard hydrogen electrode
(SHE) was initially applied which produced some
hydrogen evolution useful for removing fine amounts
of remaining concretion and corrosion products. As
the treatment progressed, the potential was reduced
to -0.750 V. vs. SHE to continue chloride extraction