Travertine fragments

Bianca Madden <bianca_madden<-at->yahoo<.>co<.>uk> writes

>Have any conservators had successful experience of pinning/dowelling
>large travertine 'Egyptian alabaster' fragments?  ...

Because calcite is a relative soft mineral, it is not necessary to
use a hammer drill: Drill bits for hammer drilling have quiet blunt
tips suitable for concrete and other hard materials.  Instead, try a
normal power drill with drill bits for ceramic wall tiles.  I prefer
this quality:

    <URL:http://www.bosch-pt.com/de/de/accocs/zubehoer/207730/mehrzweckbohrer-cyl-9-multi-construction/>

Using this, the material is more "cut" with the sharp edge than
hammered out.  You can also try HSS-drills sold to drill metal, but
they will get dull much faster.

For bigger diameters, use a small drill first and enlarge the hole
step by step.

When drilling small stone fragments, I clamp the drill machine to a
table, fix the power switch and hold the fragment in both hands. For
holes bigger than 2 cm in diameter, I use a diamond core drill. They
usually run with water, but you can also connect a hose of
compressed air (less than 1 bar) witch will do the same
job--bringing out the dust and cooling the drill.  Water produces
mud, with air cooling you got a lot of dust--depends what is less
harmful to your object.

For very fragile stones, there are also possibilities to secure the
object with a temporary wrap of rigid material like fiber reinforced
thermoplastic resin over a separation layer.

Olaf Pung
Diplomrestaurator(FH), Steinmetzmeister
Thuer, Germany


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                  Conservation DistList Instance 29:28
                 Distributed: Friday, December 4, 2015
                       Message Id: cdl-29-28-003
                                  ***