Tackling the hard parts

May 25, 2010

Annotated image of C 396, showing the fill categories.

Remember this image from our work plan way back when (two weeks ago)?  Well, we’ve now done the fills marked in green and decided that some of the ones marked in red should be green and did those.  So, what’s left: the big  fills colored yellow here, which we’ve been thinking hard about.  The fills are not structural, in that the relief is stable without them, but they’re needed to complete the appearance of the relief.  So, we needed fills that wouldn’t place any stress on the stone but would be able to support themselves, especially the top one, which is one whole corner of the relief.  The previous (1916) fill had been made using plaster, burlap, wood scraps and newspaper (which is how we know the date).  We wanted something a little more stable; that would last and would look good for decades to come, but would be easy to remove if necessary.  (This was especially important to Julie, who’d spent months removing the previous fills!).  Our answer, at least the first part of the answer was foam.

The polyethylene foam insert carved to fit in the lower gap on C 396.

Polyethylene foam is lightweight, stable, and relatively easily carved with sharp knives.  Our Chinese colleagues were a little dubious about this technique but gave us the benefit of a doubt and agreed to try.  In fact, Julie and I were not at all sure it would work either, so we decided to try the easier fill first – the smaller one at the bottom middle of C 396.  Several planks of foam were stuck together (using hot melt glue and bamboo skewers) and carved to fit into the gap between the stone segments.

Lynn and Julie mixing the epoxy resin and rolling out the ‘pizza’.

To provide a some rigidity and give a surface that could be matched to the surrounding stone, the front face of the foam would be covered with epoxy putty.  Epoxy putty comes in two clay-like parts which, when thoroughly mixed are soft and malleable but set into a rock-hard resin within 12 hours.  This was all experimental but a small test showed that the epoxy would bond well with the foam.  Then it was just a matter of kneading a lot of epoxy, spreading it into a thin sheet, which was then applied to the foam and left to set overnight.  Mr. Yang (who took all these pictures) was a great help and the language barrier was no problem as we demonstrated all the steps and then invited his participation.  ‘Ah’, he said as we were rolling out the putty, “pizza”.  Pizza: the international language!

Julie applies epoxy resin to the foam insert

The insert with its epoxy coat.