Strutt your stuff! Reducing pesky stains
A behind the scenes look at items on display in our William Strutt exhibition
23 October 2015
Many of the items on display in our Exhibition Gallery for the William Strutt exhibition, Heroes and Villains: Strutt's Australia, previously had dark orange and brown staining on their corners from deteriorated sticky tape or adhesive where it may have been previously mounted. These dark adhesive residues had begun to stain the objects all the way through to the front of the work. As this was accelerating the rate of degradation of these works, we have attempted to remove as much of the adhesive and stain as possible without causing harm to the work.
Many of the works had stains similar to the image below, and the Preservation team worked hard to reduce these stains using various gentle and careful techniques.
How did we do it?
After identifying through spot testing that the stains were responsive to ethanol, they were first reduced over a suction table to remove as much adhesive residue as possible by brushing on 100% ethanol. As direct application of these solvents did not prove successful, and the stains and adhesive residue remained very evident, a poultice of ethanol and magnesium trisilicate was used to slow down the process.
The idea behind the poultice is that the dry material (magnesium trisilicate) absorbs the liquid (ethanol) and holds it against the surface of the paper allowing time for the liquid to reach into the paper and interact with the stain. As the liquid evaporates, the stain is pulled into the dry material rather than being placed on the surface of the paper again.
This gave the stain a longer period of time to respond, with the poultice slowly drawing out the degradation products and adhesive residue through a vacuum like capillary action as it dried.
Magnesium trisilicate was chosen as a poultice component for several reasons. Firstly, for its porous structure, even in a fine powder, creating a high rate of absorbency to not only bind with the ethanol, but facilitate the gentle and passive capillary action to extract the discoloured materials without much active working time from a conservator. It also minimises surface manipulation that can occur with brush application or the pull of a suction table. The poultice is advantageous as it reduces the quantity of solvent required for an effective treatment, and increases contact time between solvent and stain.
Creating the poultice
The poultice was created to be ‘not too wet and not too dry’, mixing the inert binder magnesium trisilicate with the solvent, ethanol. Too dry and it would not have enough moisture for the capillary action, and too wet would risk creating tidelines. The mixture was then placed onto a clear, flat, solid surface (i.e. a glass weight), enabling a view from above to visualise what's happening beneath, and pushed into the shape, then placed down onto of the stain, pressing down gently to establish and allow capillary action. To avoid tidelines from creeping out beneath the mixture, a barrier of plain magnesium trisilicate can be pushed in around the edges of the poultice to absorb any leaking or creeping solvent. At this stage it is important not to move or touch the poultice before it is completely dry (usually more than nine hours) as it will lose this action and will require the process to start all over again. As tempting as it is to check how things are moving along, the final moments of drying are the most effective in pulling out those stains!
The poultice was removed after it had been left to dry overnight, and a faint yellow colour could be seen where the poultice had removed some of the components of the stain. This process may be repeated as required.