Peeling Back the Layers: Conserving the Mora Tree Watercolour

On 20 March 1838, Robert Schomburgk presented a paper entitled 'Description of the Mora Tree' at the Linnean Society, accompanied by a watercolour and specimens of the tree itself (DA/ENG/2/SP/999). It was later published in the Transactions (1839). Below, I describe the conservation work carried out on this piece.

I have recently been conserving SP/999/2/2, a detailed watercolour illustration on paper of a tree with a group of indigenous people among the roots. I found it a fascinating image. The title, in iron gall ink read ‘The Mora – Tree of Guiana’ with a graphite pencil notation that read ‘Schomburgk No 866’ and was written at the top left corner. I found the dimensions of the paper sheet to be 336mm x 467 mm, width x height. The image had been mounted onto a backing sheet lined on the recto (front) with mauve paper. I measured the backing sheet and found it to be 356 mm x 472 mmm, width x height. The iron gall ink text along the right-hand edge read ‘For the Linnean Society of London from Robert H Schomburgk’. I noted that the verso (back) of the backing sheet was a highly glazed brown paper which, in one area had been abraded to reveal the paper fibres. There was a strip of pressure sensitive tape along the left edge and the adhesive had dried out, with the tape having become detached in places. The paper the illustration was on was separating from the backing sheet. Areas of the paper were uneven and raised as numerous air bubbles had formed between the two sheets. In addition, the two sheets were separating around the edges. Where the paper was raised there was evidence of the watercolour image being worn away.

Following a discussion with Dr Isabelle Charmantier, Head of Collections, and Janet Ashdown, Conservator, a decision was made to see if it was possible to easily separate the illustration from the backing sheet. Prior to separation surface dirt on the recto of the artwork was carefully cleaned using a smoke sponge and soft eraser. The artwork was placed face down on a sheet of wet strength paper and an area 100 mm x 80 mm, width x height, in the bottom left corner was selected as the two sheets had already separated at this point. A thin pallet knife was used to separate the two sheets. This resulted in the skinning of the mauve paper lining with paper residue remaining on both sheets. A scalpel, held at a very shallow angle, was used to reduce the thickness of the mauve paper residue on the verso of the illustration. The remaining paper residue and a layer of adhesive were softened with the minimum of moisture applied on a small section of sponge and removed with the edge of the pallet knife. 

The illustration and backing sheet were interleaved with layers of Bondina and wet strength paper and placed under a light weight to dry. Given the success of this procedure and using the methods described above the artwork was separated from the backing sheet and the remaining paper residue and adhesive carefully removed from the verso of the illustration. Where appropriate, shaped or splint repairs of Japanese tissue were applied to areas of weakness or damage with Shoufu wheat starch adhesive. A mattress needle was used to shape the repairs; this exposed the long paper fibres along the edge of the repair to form a strong and seamless bond with original paper. The backing sheet with caption has been retained as it forms part of the history of this piece. The mauve lining paper was retained and where it was lifting from the surface of the backing sheet it was re-adhered with Shoufu wheat starch paste. On completion of treatment the illustration and backing sheet have been placed in individual bifolds of Heritage Woodfree Book White paper, to protect them in storage and use. The conservation of this piece took around 35 hours to complete.

John Abbott, Conservation Volunteer