Gypsum crust as a source of calcium for the consolidation of carbonate stones using a calcium phosphate-based consolidant

Comparative Study Between Ammonium Phosphate and Ethyl Silicate Towards Conservation of Prehistoric Paintings in the Magura Cave (Bulgaria)

“…In the case of "DAP", no evident sign of a wet fringe could In the case of the stone specimens, the penetration depth was 4.5 ± 1 mm for "ES" and 7.0 ± 1.0 mm for "DAP", the limit of the wet fringe being more easily distinguishable in "ES" specimens. Such penetration depth of both consolidants was in line with previous results if the porosity of the substrate was considered: a penetration >10 mm was reported for both ES [42] and DAP [26,42,62] for highly porous limestones (open porosity 35-50%), while values between 3 and 5 mm were reported for less porous stones (open porosity 5-17%) [30,40]. It is worth noting that previous studies highlighted that, during curing, consolidants are progressively absorbed into finer pores [12], so that the final depth of formation of new binding phases is generally higher than assessed right at the end of the consolidant application [38,63].…”

“…Thanks to the low viscosity of the phosphate solution and to the absence of nanoparticles, a good penetration depth is usually achieved (>5 cm in highly porous limestone) [25]. So far, the treatment has provided good results on a variety of substrates [25], including many types of natural stones [26][27][28][29][30][31][32], mortars [33,34], and stuccoes [35]. Recently, the interaction between ammonium phosphate solutions and pigments used in wall paintings has been investigated, and, in most of the cases (but not in all), the treatment has been found to cause negligible color changes [36].…”

“…This is encouraging towards the use of this treatment for the conservation of wall paintings, even though the substantial difference of the Magura cave paintings remains. Another positive aspect of the ammonium phosphate treatment is that the presence of salts in the stone pores has proven to be not detrimental for the treatment success [30,37], but, of course, this depends on the amount and type of salts and on the features of the stone pore system. Moreover, accelerated durability tests have shown that ammonium phosphate treatment is able to increase the durability of treated stone to salt crystallization cycles [38][39][40].…”

Phosphate-based treatments for conservation of stone

“…Moreover, an increasing number of studies is dealing with the possible application of the phosphate treatment to additional substrates, such as sandstones [26], gypsum [27], archaeological wall paintings [28], and archaeological bones [29].…”

Inspecting adhesion and cohesion of protectives and consolidants in sandstones of architectural heritage by X-ray microscopy methods

“…Imaging and microanalysis techniques usually represent the best basic approach for studying textural, structural and compositional features of natural stones [1][2][3][4][5][6][7][8][9]. As regards the analysis of the interaction between stones and conservation products, SEM-EDS studies are widely employed, giving relevant clues on the location of the products inside the porous matrix of stones and, in particular, on their penetration depth [10][11][12][13][14][15][16][17][18]. However, when the in-depth investigation of the structural arrangement of these products is concerned, this approach may fail to provide unambiguous answers.…”