The Marriage of Strongbow and Aoife is painted on a single piece of linen fabric made from a twill weave. Different canvas weaves can vary the surface of a painting as the pattern of the fabric support projects its surface onto the ground and paint layers. Most fabric supports are tabby wave, which creates a regular painting surface. Twill weaves are more rarely used and generally associated with the 16th century Italian school and the 18th to 19th century English schools. It is generally anticipated that paintings of this size and date are made from a combination of fabrics stitched together. Unusually, Maclise painted The Marriage of Strongbow and Aoife on a single piece of cloth: this is uncommon for a painting of this size and date, as the type of loom needed to make a single piece of fabric this large would have been very rare in the early 1850s.
When treatment of The Marriage of Strongbow and Aoife was originally proposed one of the main concerns of the NGI conservation team was the instability of the canvas. From the initial visual examination it was possible to establish the tacking margins of the painting were very weak. Tacking edges are often more damaged than the rest of the canvas because the rusted tacks and resinous wood can accelerate oxidation and embrittlement of the canvas. Ethically the practice adopted by conservators today is to intervene as little as possible, however, when a canvas is over one hundred years old and showing signs of deterioration some level of intervention is necessary.
Removing a canvas from its stretcher is never undertaken unless it is absolutely necessary, as this type of intervention can present many risks to the painting, such as damaging the tacking edges which may not be strong enough to allow re-stretching. When conservators are presented with this level of deterioration a treatment called strip-lining is undertaken to stabilise the tacking margins. This process involves the application of a strip of canvas to reinforce the original edges of the painting. Strip-lining is often done with polyester canvas and BEVA adhesive (ethylene vinyl acetate copolymer) and has proved to be effective over many years.
Due to the level of deterioration throughout its tacking edges The Marriage of Strongbow and Aoife was strip lined in order to stabilise the painting. Prior to this treatment the painting was removed from its stretcher, the edges were lightly cleaned and the holes and tears were repaired. Polyester margins were then adhered to stabilise the degraded edges of the painting.
This treatment involved application of polyester strips which had been painted with a layer of Beva adhesive. Beva adhesive is activated by heat which was applied to the edges of the painting with a specialist conservation iron that has a finely tuned thermostatic control. This ensured the margins were adequately heat sealed to the original canvas to take the load of the painting without any adverse effects on the original support.