dk nkf - Nordisk Konservatorforbund Danmark

When working on the objects from the Open Air
Museum’s houses it was obvious to test protection
of our painting procedure where the topcoat has to
give the illusion of old iron surface. Graphite alkyd
paint coatings look much as old iron when mixed
and retouched with shades of black alkyd paint, but
would a topcoat with likewise shiny aluminium/
zinc spray (or a spray with stainless steel particles)
function better? For the quick test (Fig. 6A-B) our
procedure of 4-5 layers was minimised to three, to
give a worst-case situation. To compare with these
the lower right corner got a layer of clear acrylic
coat product from Cortec (Cortec VCI 386).
The steel panel for the quick tests seen in figure
6A, was first lightly sandblasted on one side.
(Sandblasting is standard procedure before
application of paint systems for outdoors.) Three
sections of the panel were painted by brush with a
layer of zinc-containing primer, Rust-Oleum 1080,
and then the following different paints were applied
in two layers:
• Top left: a coat of Rust-Oleum 7500 was
then applied, because it is known to seal well
when used as top coat, and over that again the
graphite-containing alkyd paint.
• Bottom left: only an extra coat of the primer
was applied and then the graphite-containing
alkyd paint.
• Top right: the Rust-Oleum 7500 was applied
and then a spray paint from the same company
containing both aluminium and zinc. (Its shiny
appearance could always be altered with black.)
Horizontal lines have been scratched through the
coatings with a scalpel blade so their later protection
when physically altered could also be seen. After one
month’s exposure outdoors, the clear coated corner
is starting to deteriorate, while the painted regions
are stable – even where the paints are scratched
through (Fig. 6B).
Encouraged by the paint’s abilities, three full panels
were coated and sent for accelerated weathering
tests (being supervised by the mentioned colleagues
for their tests). Following this the same types will
also now be included in the connected long-term
outdoor tests. We decided merely on two differences
to the above-described procedure. The steel panels
were only degreased, as were the panels they here
will to be compared with. The top spray paint from
Rust-Oleum now used contained stainless steel
particles (which resembles iron more) instead of Al/
Zn. When ready, the final results and comparison to
evenly applied clear coatings will be published.
Testing a decision making
model
Hopefully the ongoing tests at the National Museum
of Denmark will help us to make more confident
choices for protection of cleaned iron and maybe
even to protect rusty or partly de-rusted iron.
Museum staff in the future should be able to make
reasonably realistic predictions of a treatment’s
protection time, and in choosing, be aware of costs
of any needed follow-up maintenance. Making
decisions is important and requires systematic
judgment.
As of now, if you only wish to partly remove rust
layers and are not willing to fully clean and coat iron
(oil, wax or paint products) the object has to be kept
at very low relative humidity. It may be desired to
save remains of original paint layers or iron may be
an integrated part of a composite construction that
cannot be treated separately. In these cases iron can
be embedded so that rusting mostly happens where
it is unseen and least treatable. Decision-making
for iron conservation is not easy because there are
several important issues:
1. The main conservation factor is the object’s
preservation and, thereby, chemical and
physical stability – The iron surface has to be
quite stable even if the surrounding RH is not
very low. Large metal objects are sometimes
submitted to more physical handling than
museum staff generally considers. The
coating’s strength, therefore, is also an issue.
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