Bronze

Mark Vine <100436.3447 [at] compuserve__com> writes

>The question raised by the conservator is whether salt (from a
>century of sea air/water pounding) could have penetrated the pores
>of the bronze and whether it might now be being released to
>contaminate the surface below the lacquered surfaces.

It is certainly possible that salts embedded within the bronze are
affecting the adhesion of the coating.  It may depend on several
factors.

The methods of removal and (I presume) repatination were not
disclosed but should be studied to determine if they left residues
which could cause this problem.  Window frames, as opposed to
surrounds, are generally of fabricated bronze stock rather than cast
bronze.  Castings tend to allow for the porosity that encourages pit
corrosion which might continue to hold salts if not adequately
cleaned.  If, however, these windows are fabricated of stock then
the likelihood of pit corrosion due to porosity is remote.

Direct battering by wind borne salt can create pitting even in
extruded shapes but, as there is no underlying flaws to retain the
salts, if the metal was adequately cleaned then these should not
continue to cause problems.  Lacquer application methods may lead to
this condition.  If the metal was cold and shaded, for example,
condensation can cause a layer of moisture which will inhibit good
adhesion of the lacquer.  If the metal was pitted and the lacquer
sprayed on only, the lacquer thickness can become very thin over the
pits due to their larger surface area relative to adjacent smooth
surfaces and pin point failures can occur.

Finally, I have seen an Incralac coated treatment which failed for
no discernible reason. The manufacturer should be contacted but, as
the recommended use of their product is on new, fully cleaned metal,
they are not likely to warrantee this type of installation.

Mark Rabinowitz
Conservation & Sculpture co.

                                  ***
                  Conservation DistList Instance 12:88
                   Distributed: Tuesday, May 18, 1999
                       Message Id: cdl-12-88-002
                                  ***