Canvas lined with lead adhesive

I am currently working on two late seventeenth-century canvas
portraits that have been previously lined with an unusual adhesive
and technique. The adhesive is orange in colour and consists of an
inorganic material containing lead and iron pigments and oil as a
binding medium. The presence of leadsoaps, iron-oxides and oil has
been confirmed.

The lining method seems to have been as follows: the lining canvas
was attached with tacks to the strainer and coated with the lining
paste. Afterwards the lining paste was applied irregularly either as
a second application to the lining canvas or onto the reverse of the
original. The original canvas was then attached separately with
tacks to the strainer. It is presumed that the two canvases were
bonded together with use of pressure and possibly heat.

The lining paste has migrated through the cracks in the ground and
paint to the surface, thus it must have retained its fluidity for
some time. Over the course of time much of the lining adhesive has
become brittle and in large parts the adhesion between the two
canvases has failed. During the removal of the lining canvases it
was noted that some thicker areas of the adhesive had remained tacky
and soft.

This does not look like the 'typical' lead-lining as far as I have
found references to this technique

    C. Keck, Handbook on the Care of Paintings

    U.H. Vrana. Alternatives for traditional relining

    K. Nicolaus. Handbook for Restoration

Has anyone come across a similar lining technique or know of any
possible origin or dating for it? Photos and technical information
would be most appreciated as would any advice on the conservation
(re-lining) of paintings lined with a lead based adhesive.

Nada Miedema
(student Conservation of Easel Paintings)
Stichting Restauratie Atelier Limburg (SRAL)
Postbus 1679
6201 BR Maastricht
The Netherlands


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                  Conservation DistList Instance 22:43
                Distributed: Saturday, January 31, 2009
                       Message Id: cdl-22-43-031
                                  ***