February 2010: Mending begins

May 10, 2010

Annotated photograph showing planned mends for C 396. Black lines indicate acrylic adhesive joins; blue lines indicate epoxy adhesive without pinning; red lines epoxy adhesive with pins; grey rectangles indicate approximate placement of steel pins

Finally, in February, it was time to start putting the reliefs back together.  There were three levels of joining: small mends; medium mends, and major mends.  For us conservators, the medium and major mends had been a matter of discussion since the earliest phases of the project.  Our original plan was to use reversible adhesives with no dowels, in keeping with ideal conservation practice.  Conservators prefer to maintain the principal of ‘reversibility’ – doing nothing to an artifact that can’t be undone at a later date.  We also always try to use adhesives and other materials that stay stable over long periods of time.  Epoxies, the adhesives most often used in Joining stone are not reversible and tend to discolor over time.   Worse yet, traditional stone joining methods often involve inserting steel rods as dowels between the pieces to be joined, which would require drilling out channels in the stone.   We were very reluctant to do anything that changed the original artifact significantly, even though the channels would be completely invisible once the joins were made.  When we mentioned this to our rigger, Harry Gordon, who regularly joins large pieces of stone in his artwork, he just smiled pityingly at our innocence and said “hmm”.  A colleague in Penn’s Historic Preservation program was more forthright: ‘that’s not going to work’.  Gradually we came to accept the inevitable – we would need to use epoxy adhesives and steel rod dowels if the major joins were to remain stable.

Block being drilled using a water-cooled drill. 21 Mend2. Caption: The first join being made, with steel rods protruding from the lower fragment and epoxy adhesive being applied to the join surface

We then needed to find specialists with expertise in this area, since we had never drilled and pinned large hunks of stone before.  We contracted  with the local historic preservation firm of Milne+Carr, who would drill the channels in the stone and make the major joins that would also require the services of our riggers again.  Before then, Julie made some of the smaller joins, using a reversible acrylic adhesive on the smallest pieces and a non-reversible epoxy on the larger sections.  A conference between the all the involved parties (armature designers, riggers, specialists who would be doing the drilling, and us) before we started the process finalized our mending plan.

The Completed Join

We began the drilling and pinning phase of mending on March 1, 2010 planning to have it done within three days.  As with most phases of the project, unexpected complications meant that it took longer than anyone expected.  However, after much anxiety and hard work, each relief was joined into three large segments.

Drilling for armature

There was one more task for our drilling specialists.  The way in which C 396 had fractured made its armature especially tricky.

Detail from armature design, showing bracket to be used to attach large unsupported segment to armature

The central ‘pie-shaped’ fragment, which weighed almost 3000 lbs, had very little to support it, except where its weight was borne by a few small areas of the other two fragments.  It was this fact, more than anything, which had led to the instability of the whole relief.  The only way to support this weight without putting enormous stress on the other fragments was to find other method to support the weight.  The armature design called for a large support structure from which the segment would be hung, its weight supported by the steel and not the underlying stone.  This would require drilling two angled holes in the back of the segment into which a steel bracket could be  inserted.  Despite our reluctance to make permanent changes to the back of the relief, there was no other way to provide adequate support for the stone.  This would require extremely precise drilling to match the angle, spacing, and alignment of the  bracket inserts.  Again our riggers’ expertise in stone techniques was a great advantage as they provided suggestions for the preservation conservators doing the drilling.

Adam and Jay triumphant as the bracket fits in the drilled holes.

In the end, everyone’s careful preparation paid off, although the holes had to be slightly adjusted as they were too precisely drilled to match the steel bracket, which was slightly misaligned!