Conservation of glass plate negatives in
the British Steel Collection
During the late 19th and early 20th Centuries photographic negatives were made from sheets of thin glass with a light sensitive emulsion applied to one side. In the early days of glass plate negatives, the photographer applied the emulsion immediately before taking the image so the plate was exposed while still wet. Commercially produced plates were soon available which had the emulsion pre-applied and could be used in a dry state, these are known as ‘dry plates’.
Once fixed the plates could be treated with varnishes for protection or under go re-touching or formatting processes involving the painting out of areas with opaque paints or picking out details with a pencil. From these negatives positives were made by placing photo-sensitive papers under the glass and exposing to light.
The British Steel Collection is home to over 6,000 glass plate negatives of various sizes from 15 x 12 down to 3 x 3 inches. Luckily the vast majority are in good condition but they are susceptible to damage and deterioration from many sources: The most obvious and problematic is physical damage in the form of breaking of the glass support or damage to the image layer from grating. Plates are often stored in the original boxes in which they were purchased, in these they lie flat sometimes placing a lot of weight on the bottom plates and allowing movement and abrasion if the box is too loose. Additionally these boxes are nearly always made from materials that are potentially damaging to the images. The image layer is vulnerable to attacks from mould often following water damage, this can cause the emulsion to flake off from the glass leading to areas of loss in the image. Fingerprints on the emulsion are difficult to remove and will damage the image.
Standard procedure when dealing with glass plate negatives in generally good condition is to dust with an extremely soft squirrel hair brush then to place each individual plate in a folded enclosure made from a paper specifically designed to store photographic material. The plates are then grouped together in small batches and boxed in such a way as the plates stand on end rather than lie horizontally. However, if the plate is broken in multiple pieces, has missing pieces or has a weak and flaking emulsion layer, a different approach is needed.
Treatment of damaged glass plate negatives
This is a large glass plate negative measuring 12 x 10 inches showing a family group posed around a table on which appears to be a photograph album.
The most striking thing about this image is the amount of red paint applied to remove the background. This paint was extremely powdery and loose with flakes falling off every time the plate was handled, these flakes had found their way onto the emulsion side of many other plates housed alongside it and were adhered where they landed. At some point water had been got onto the plate causing the paint to run onto areas of the image intended to be visible. This was most visible across the dress of the girl on the right of the image. The top right hand corner had been broken off but was present.
By placing the plate on a light box it was possible to see a defined line where the edge of the paint had originally been, it was decided to remove the excess paint but leave the rest as it was the intention of the photographer to paint out the background.
Firstly the remaining red paint at the top and left-hand side of the image was consolidated using an adhesive (Methyl cellulose) this stuck down any flaking areas and sealed the surface stopping the loss of the powdery top layer.
Many flecks of the red paint had scattered across the glass side of the negative and had become adhered. These were removed using a cotton wool swab dipped in a mixture of solvent (industrial methylated spirit) and water. Then all the areas of the glass side not covered in paint were cleaned in the same way.
The image side was only brushed, no further cleaning was carried out on this side due to the risk of further damage to the emulsion.
Once cleaned and consolidated, the plate was re-housed in a sink mat enclosure made from photographically compatible mount board. The plate sits in this enclosure which has a rigid base board, walls higher than the plate and a hinged solid lid. Each sink mat is made to fit a specific plate as a firm fit is essential in order to stop the glass moving around and damaging the emulsion that is placed facing the baseboard. There are two gaps in parallel sides of the walls to allow access to the side of the plate to help with removing it.
The negative is now stabilised ready for digitising. Areas of scratched emulsion and missing opaque paint can be corrected on the digital version of the image while the original goes into storage. Having a high quality copy of the image means the glass plate can be retired from use thus eliminating the main risk of damage, that of handling.
Inverting a photograph taken during conservation on the light box gives an indication of how the image will look after digital manipulation.
This glass plate negative has suffered physical damage probably due to its large size. At 15 x 12 inches the plate is difficult to handle and store due to its weight and brittleness and this may have lead to a large section of the bottom left corner breaking off and the loss of a smaller section along the top edge (lost). The fragment was attached to the rest of the negative using pressure sensitive tape. It shows a group of men in identical formal dress, a prominent man is holding a baton indicating this may be a band. There are small areas of loss to the emulation layer, the most noticeable being one of the face of one man which may have been removed deliberately.
Much less conservation is required to this plate than was needed for the previous one but this plate needed a more complicated housing method. Firstly the adhesive tape applied as a temporary fixing method was removed with tweezers. Cleaning of the glass side using IMS and water removed a good deal of dirt and no treatment took place on the image side due to the delicacy of the emulsion.
Again a sink mat was made for the plate but with some modifications. Firstly the base and lid were made from a double thickness of board laminated with the grain directions crossing in order to make as stiff a structure as possible to help support the weight of the negative. The broken corner has been separated from the rest of the image by small spacers in order to stop grating and damage to the delicate broken edge.