Konserwacja kamiennego portalu z Ołbina w kościele Marii Magdaleny we Wrocławiu

The Romanesque doorway from Ołbin whose origins may be dated as early back as to the late 12-th century was built from blocks of arkose sandstone. During the long course of history its state of preservation gradually deteriorated and thus it had many times to be subjected to conservating treatments. Its surface was, among the others, reinforced by means of liquid glass and chemicals of the fluosilicate group. It seems, however, that the treatments applied did not bring intended effects and this probably was the reason why one part of the doorway has been coated with cement milk whereas the others co-ered with a protective layer of a hardly distinguishable polymer-type organic matter. Nevertheless, these superficial coatings have proved to be unable to prevent advancing decay and the stones were getting more and more disintegrated, maybe at even higher rate as it was the case at earlier date. Finally, the layers next to the stone surface begun to split and exfoliate and from underneath poured the powdered sandstone. This increasing decay has led to substantial decrements in the total mass and also to deformations in the plastic appearance of the doorway. In effect of investigations carried out it became possible to find that these destructions were, in the first line, caused by the action of water-soluble salts and water penetrating into the doorway from the church interior which the both occurrences were due to the fact that the outer surfaces of walls have been faced with clinker bricks hardly permeable for water. Although several expert bodies were meeting with this object in mind no clearly outlined programme of preservation works for the said doorway has been worked out in conclusion. The works carried out within the first stage comprised the following measures: encasing of the doorway to protect it against the immediate weather influences (mainly the waters'), securing the fragments by glueing the paper on their surfaces, removing the clinker bricks from the immediate neighbourhood of the doorway, and, finally, building of a cellar under it to stop the flow of ground waters. The undertaking of a full-scale treatment has become possible only on completion of examination of possibilities to apply epoxy resin solutions for structural impregnation and also on working out of the s.c. pocket-type method for stone saturation. Investigations in this respect were conducted at the Copernicus University, Toruń to order of the Historical Monuments Documentation Centre, Warsaw. The conservating works themselves were carried on in the years 1967 and 1968 and their plan covered the actions named below: a) superficial strengthening of pouring, delaminating and exfoliating portions of stones from which the doorway is built, . b) reinforcement of the breaking away fragments of doorway with the application of putties and fillings, c) removing of the superficial built-up layers with the aim to restore the stone porosity and ipso facto enable the impregnation, d) removing the cement and gypsum putties and fillings by means of which the former decrements in stones were filled up, e) extraction of water-soluble salts, f) structural impregnation of the entire doorway with the aim to reinforce the deepest stone layers, g) filling with putties the holes and pin cracks. The superficial reinforcing of stones was carried out by means of the 20 per cent methylbenzene solution of epoxy resin. The resin was hardened by treating it with triethylenetetraamine. For reinforcing of stone fragments that have broken and exfoliated thus threatening to flake the putty has been applied obtained by mixing the epoxy resin with powdered sandstone in 1 : 15 proportion. The putty was filled into pin cracks and then pressed. With the putties hardened a durable junction was obtained between the loose fragments and their bed. Thanks to the properties possessed by existing built-up layers they could be removed with the use of either chemical or mechanical means. Chemically were removed the layers formed in result of an usual action exerted by atmospheric components, and the 3 to 6 per cent hydrofluoric acid was applied for this purpose. Portions on which the afore-mentioned built-up layers have been found comprised well under 10 per cent of the total doorway area. The layers consisting of cements and organic matter not soluble in solvents available were removed mechanically by means of scrapers. With the dark-coloured built-up layers removed the stones of which the doorway is composed have regained their original colour, texture and plasticity. (However, it has proved impossible to restore to the superficial stone layers their original porosity. The reinforcing substances with which the stone pores were filled are unremovable and their porosity could be restored only by means of grinding-off the superficial layers being, of course, an inadmissible practice. The cement putties and some gypsum putties, too, applied during the former restorations of the doorway were removed, for they contributed to the accelerated destruction of stones, in addition forming black spots on the brighter coloured background. On completion of the above-mentioned works the next stage has been started, consisting in removing of water-soluble salts. A method of their forced migration to paper layer was applied using the fivefold coating of the entire doorway with water saturated paper sheets. Already the fourth consecutive paper coating did not reveal the presence of salt. The above method allowed to remove the salts from pores next to the stone surface which the fact is due to limited permeability of water into the deeper stone layers in effect of earlier applied treatments (N. B. migration of salts occurs only in parts saturated with water). As the superficial impregnation of doorway carried out by means of epoxy resin solution is able to prevent decay for a limited period of time only it has been decided to reinforce the structure of the doorway stones in their deepest possible layers (structural impregnation). This treatment was carried out using 10 per cent toluene-and-methyl alcohol solution of epoxy resin in the respective proportion of 1 : 2 and 1 : 3. The amount of methyl alcohol present in 'Solution was deciding for the rate of resin precipitation from it. At the 1 : 2 proportion the precipitation was beginning after about 20 hours whereas at 1 : 3 after about l'O hours. The first of the above solutions was applied in cases in which the need occurred to saturate the stones for more than 12 hours, the other one — for saturation periods not reaching the time given above. Solutions were prepared in portions of 1 to 4 litres to which 15 per cent of triethylenetetraamine was added in proportion to resin amount. They were introduced into the doorway stones by means of s.c. pooket-type method. The pockets were prepared in such a way that on the stone surface were put 5 to 6 layers of the water-saturated paper onto which, starting from their edges, the gypsum mortar was imposed forming the 1 to 2 cms wide framing at all sides. In the upper parts of so formed lining a filler was made from a piece of paper and the whole covered with gypsum . The separate stages of the pocket-forming may easily be seen from illustrations. All the elements of doorway were covered with pockets. With the gypsum mortar dried the tightness of pockets was examined by means of solvents and leakages removed. The impregnation has been carried out by pouring the solution into pockets and its steady supplementing so that the pockets could be kept full throughout the entire period of saturation. During one-day operation were saturated the doorway elements with sizes allowing to complete saturation and removing the pockets themselves within 30 hours. It has been found that within this period the epoxy resin gel forming in gypsum pores was still thin enough to enable the easy removal of pockets. They could be removed without damaging the stones as the object after impregnation was secured with cellophane having inhibitory effect on evaporation of solvents. Since the rests of gypsum remained on the stone surfaces they had to be removed at once thus not permitting their hardening by the active resin. After cleaning operation the saturated elements were insulated by means of cellophane from the ambient atmosphere for a period of 10 to 14 days to allow the maximum rate of precipitation of resin from the solvent. Three hundred ninety litres of resin solution were used for this purpose of which the amount some 295 litres have been introduced into stone, the balance being absorbed by gypsum and lost during the operation. Within the last operation the supplementing of slight stone decrements in form of holes and pin cracks with the epoxy putties has been carried out. For this purpose, much the same as in the course of the above-described operation, a mixture composed of 1 part of epoxy resin and 15 parts powdered sandstone has been applied. To this mixture containing hardener (15 per cent) petroleum spirits were added to obtain better conditions for hardening. The putties prepared for this operation are characteristic of their higher degree of porosity at the same time showing good water-repellent properties and impact strength similar to that of actual stone. For preparing the putties the white sandstone powder was used so that after their hardening it proved necessary to patinate them together with traces left by pockets („crabs”) using mineral dyes with 1 per cent addition of epoxy resin solution acting as hardener. The illustrations show the doorway in state after preservation operations.