Marble plaque

Debra-Kay Palmer <debbiepal99 [at] yahoo__co__uk> writes

>I am a Conservation Officer treating a marble plaque, which has lead
>used to fill in the space of the letters. However, some of the
>letters have fallen out and I'm not sure what can be used to replace
>these lead letters. Does anyone have any suggestions about what
>could be used, something that could also survive daily exposure to
>the sun.

Two factors are particularly important in choosing the type of
gapfill:

    a)  is the plaque vertical or can it be laid face up on a
        horizontal surface?

    b)  were the letters cast from lead and then attached to the
        stone (usually by small pegs jutting out of the back of each
        letter being pushed into holes drilled into the stone in the
        centre of each letter space) or were they formed from molten
        lead poured into letter spaces cut in the plaque?

If the letters were cast from lead and then attached, it would be
possible to make moulds with two-part silicon rubber, either from
loose letters which are already detached, or from replica letters
made to match from plasticine, wax or a suitable modelling clay (one
which does not contain water). Don't forget to include the little
pegs at the back or whatever mechanism was used to attach the
originals to the marble.

Polyester resin can be tinted to give a very good match to aged lead
and can easily be cast in simple moulds. When set, the letter is
then sanded or shaped to remove any flashing or sharp edges, then
attached using a suitable adhesive such as Paraloid (Acryloid) B48
(for hotter conditions) in acetone. Make up a batch of coloured
resin and catalyse some of it so that you can see the finished
colour before you use it on the object.

If the lead was poured into shapes carved into the marble, rather
than being cast as letters and attached, and if the plaque can be
laid horizontally, then you may want to cast the polyester resin in
situ.  Please be very careful with this as the stone is easily
stained. In such a case I would recommend

    a.  protecting the whole of the stone, only exposing the area on
        which you will be working

    b.  coating the area which will have the resin poured in with a
        protective barrier layer of Paraloid B48 in acetone. This
        should be allowed to dry before the resin is poured in. Make
        sure there are no undercuts which would fill with resin and
        cause it to become locked in place when set. If there are
        deep cracks or undercuts you may want to fill them with
        Paraloid B48 mixed with a suitable filler such as glass
        microballoons or even modern marble dust. Fill the space
        with the polyester resin very slowly and carefully from a
        pipette, taking care not to overfill.

If the plaque is vertical and cannot be removed and laid
horizontally for treatment, then it will probably be best to cast
letters from resin and attach them with Paraloid. If that is not
possible, it may be feasible to tint a two-part epoxy putty to match
the lead and create the letters in situ. A barrier layer of a
suitable substance such as Paraloid B48 is vital in such a case.

Both epoxy putty and polyester resin should last for many years,
even in tropical conditions. The surface may eventually discolour,
but the barrier layer can then be dissolved, allowing the replica
letters to be removed and replaced.

Hope this helps,

Helena Jaeschke
Conservation Development Officer
+44 1392 665951
Royal Albert Memorial Museum
Queen Street
Exeter EX4 3RX


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                  Conservation DistList Instance 20:38
                Distributed: Wednesday, February 7, 2007
                       Message Id: cdl-20-38-003
                                  ***