Prékopa Ágnes (szerk.): Ars Decorativa 31. (Budapest, 2017)
Kornélia HAJTÓ: Restoration Options for Architectural Ceramics
veals little about its composition: ‘Product containing sodium carbonate and special components.’ Its pH is given as 11. It is always important to obtain the safety data sheet from the manufacturers, which usually gives further information on the product’s composition. Other products on the market are made by Sika, Mapei and Wehat. All share the ba- 4 4. a-b Trial cleaning on a fagadé element of the Museum of Applied Arts. There was very little cleaning effect. Photo by Kornélia Hajtó sic operating principle that a medium nonneutral pH can weaken the bonds among contaminating particles and between them and the surface. Great care has to be taken in choosing a cleaning agent, because there is no guarantee that any specific faţade element will withstand the use of a specific product without damage. The manufacturers often do not reveal the product’s constituents, which means that we do not know its precise mechanism of action. We have to make a trial cleaning and, if it is successful, carry out a microscopic examination of the surface. For a porous, unglazed ceramic, it is also important to determine whether the chemical residues can be completely removed from the pores, and if not, to find out what long-term effects they are likely to have. Perhaps the most widespread cleaning procedure is sand blasting.2 This consists of directing particles of specified size and hardness at high pressure towards the surface to be cleaned. The process may be wet, in which case a high-pressure water jet is applied along with the particles. The cleaning effect is due to the kinetic energy of the impinging particles, which disrupt and drive off the contaminants. Sand blasting is widely used on brick and stone fagades and metal and stone sculptures, and is sometimes suitable for cleaning exterior ceramics. A great advantage of the technique is its adaptability: the size and hardness of the particles and their velocity may be experimentally adjusted to achieve the greatest effectiveness for removing particular kinds of contamination from particular building surfaces. Tests on unglazed pyrogranite have found that removing dirt by sand blasting sometimes causes damage to ceramic surface. Any application on ceramics should therefore be preceded by trial clean98
