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