My Print has Pimples!

My Print has Pimples!
Treatment for nature prints from the Bradbury and Evans printing house from London
25 September 2012

Recently, the Pictures staff here at the National Library delivered 36 nature prints to Preservation Services for treatment. These beautiful examples of nature prints are from the renowned Bradbury and Evans printing house from London. Nature printing has been a popular printing method since the Middle Ages and has long been appreciated as a scientific tool for documenting plant and fish specimens. Plant and fish specimens are used to print from directly, capturing as much botanical and scientific detail as possible. Refining the process of nature printing to produce detailed copies of specimens was a competitive business for printing houses, resulting in a number of patents for nature printing processes throughout the 19th century. Nature printing can take three forms; lithographic, direct and indirect. The Bradbury nature prints we are currently treating are examples of an indirect method that Bradbury employed at the time, and is rumoured to have adapted from the process used by his mentor Alois Auer. The printing of these nature specimens utilised the intaglio printing method whereby a copper plate mould would be created through electroplating. The printing process involves making a cast of the nature specimen using a lead plate and a steel plate. The whole system is run through a press, creating an impression in the softer lead plate of the nature specimen. This lead plate is then placed in an electrolytic bath that contains copper salt. The bath is connected to the negative terminal of a direct current power supply. When the current is sent through the bath, a copper shell is plated onto the lead plate mould through electrolytic deposition. From this process two copper plates are made, the first in relief and the second forming an intaglio plate. The copper intaglio plate was then inked. If more than one colour was required, the darkest ink would be applied to the plate first, wiped back and then the additional lighter colours were added to the plate. The printing system would have consisted of the following:

Printing process diagram: Roller, Blanketing/Wool felt, Wet paper, Copper intaglio plate containing ink

After researching the printing process for these prints, the next step was to develop the treatment approach. All the prints were in relatively stable condition, however they were quite dirty and they all have the same strange paper pimples!

Image of print

The Lady’s Mantle print prior to treatment.

Close up image of print

The paper pimples up close and personal! The Common Hart's Tongue is currently being treated, however all of the prints have this odd pimply surface.

The conservators at the Library are still doing testing to identify the cause of these little bumps, which appear to be consistent with old water staining on the works. Our adopted approach was to start with cleaning off loose surface dirt. After testing the inks for solubility, the prints were then immersed in conditioned deionised water with a pH of 9.

Pre-wetting the print

The pre-wetting phase before the immersion wash.

Print being placed into the bath.

Into the bath.

This process helps to release any further dirt that may be in the paper and greatly reduces old stains. The immersion bath also dissolves and dissipates the hard encrusted core of the tiny paper pimples. Once the prints are removed from the bath they are taken immediately to the vacuum suction table, where the pronounced paper fibres are burnished back into place with a septum elevator.

Print being placed on the suction table.

The item is placed on the suction table while still damp to finish the treatment.

Print being burnished.

Burnishing the disturbed paper fibres with a septum elevator.

After all of this, the prints are then flattened between blotters and felts. Once dry, the edge tears are repaired with starch paste and Japanese hand-made tissue.

Close up detail of print.

The Dog's Mercury print with partial edge repairs and infills made from cellulose powder and starch paste.

Close-up detail of the print.

The Dog's Mercury with completed edge repairs and infills. This print had a similar pimple effect across the surface as featured in the image above.

Once all of the prints have been treated, and the cause of the paper pimples identified, they will be returned to the collection for the public to access and enjoy. The conservators at the Library hope to diagnose the cause of the paper pimples soon and add further to this blog. We would like to thank those conservators who have already assisted with their time and knowledge in attempting to diagnose the cause of the paper pimples. We would also like to thank members of the Nature Printing Society who assisted with background information regarding these prints and the printing process. In the mean time, if you know anything further about Henry Bradbury’s patented nature printing processes or if you would like to share your knowledge of nature printing, we would love to hear about it! Please just add to the comments field below to share your knowledge.