The workshop for the analysis and intervention of mural painting of the Institute for the Restoration of Heritage of Valencia (IRP) carries out a meticulous study on the behavior of pigmented ink transferred on mural plaster. This is a summary of the tasks carried out:
INVESTIGATION AND EXPERIMENTAL DEVELOPMENT OF THE BEHAVIOR OF INKJET INKS ON LIME MORTARS AND OTHER PICTORIAL SURFACES.
Different studies support the stability of inkjet prints with pigmented inks on various supports, but there is no evidence of their behavior on lime mortars, since the application is unprecedented in the world.
The Papelgel transfer system requires that the originally liquid ink dry (solidify) on the temporary support, be dissolved again and be permanently fixed on the wall surface. This change of state or the fact that the wall surface of lime and sand maintains a strongly alkaline PH (13) for a long time, are factors that could alter the stability of the whole. To resolve these doubts, studies were carried out to confirm the suitability of the pigment ink / wall plaster structure.
A large number of specimens were subjected to cycles of accelerated artificial wear (UV lighting, temperature, humidity and contaminated atmospheres) and both the comparative chemical analyzes and the evaluation of changes in color difference (DE *) and gloss gave satisfactory results, finding for example, more weakness in the wall support than in the inks in the case of the contaminated atmosphere test.
On the other hand, comparative tests of resistance to abrasion were carried out, which allowed evaluating how the structure reacts to factors such as erosion, friction, etc. It was possible to conclude that transfers in general have a moderate resistance to abrasion compared to a pictorial surface made in fresco, but very similar even superior to surfaces made dry with watercolor, which is the most used medium in restoration.
From the chemical resistance tests it was found that the transfers are sensitive to high polarity solvents such as toluene, and to a lesser extent to water.
The oldest specimens (2 years) have greater chemical resistance than the most recent ones (3 months); that is, due to the gradual setting of the lime mortar, as well as the curing of the binders in the inks, the chemical resistance of the transfers increases over time.
Contact sponge absorption tests were also carried out to objectively confirm that the transferred ink does not constitute a barrier to the natural perspiration of the lime and sand plaster.
The contact sponge methodology -developed by the CNR-ICVBC of Florence- has been proposed as a simple and quick method to assess “in situ” the effectiveness of a water-repellent treatment on stone surfaces.
The method is based on weight differences according to the formula:
Wa (g / cm2. Min) = (Pi-Pf) /23.76 x t
Where (Wa) is the amount of water absorbed during the test.