PROCESS FOR THE REPRODUCTION OF WORKS OF ART IN LITHOID MATERIAL

Abstract: Process for the reproduction of works of art in lithoid material, comprising the use of silicone rubbers to obtain a negative mould of the work of art, characterized in that a thin layer of a fluorinated grease based on polytetrafluoroethylene and of a liquid perfluoropolyether is applied to the work of art beforehand.

Description: The present invention relates to the reproduction of sculptures in lithoid material, terracotta or stucco. The reproduction of sculptures by modelling scagliola gypsum into nogs, the overlap of which permits a negative mould of the work of art to be obtained, is known. So as to obtain an easier release of the gypsum nogs, aqueous solutions containing high concentrations of soaps, or oils and/or greases are applied onto the modelled or sculptured surfaces of the work of art before the mould is modelled. The drawback of this method of reproduction is that the procedure requires a long time and, above all, an alteration of the surface of the work of art is caused in that the oils, greases and soaps used are absorbed by the material constituting the work of art and the subsequent wash cannot completely remove such substances since these materials are absorbed by the lithoid material. Remarkable improvements over the operation mentioned above have been achieved by using silicone rubbers as material for modelling the negative mould instead of gypsum. With this technique, a very faithful reproduction including even the most minute details of the work of art and an easy release are obtained and the time required by this process is much shorter than that required by gypsum modelling. This modelling method, however, has the drawback that it leaves an oily residue which is not compatible with the aesthetic requirements for works of art. In fact, this residue can no longer be removed by the solvents which are usually employed to remove silicones and which are compatible with the material of the work of art. The oily residues remain on the work of art, causing a change in colours or, at any rate, a change in the aesthetic appearance. Furthermore, the residues create complications during subsequent restoration in that, with time, they are absorbed by the material of the work of art. The object of the present invention, therefore, is a process for the reproduction of works of art in lithoid material, with the use of silicone rubbers to obtain a negative mould of the works of art, characterized in that a layer of a fluorinated grease based on polytetrafluoroethylene and on a liquid perfluoropolyether having neutral (chemically inert) terminal groups, is applied on the work of art before the application of the silicone rubbers. Any liquid perfluoropolyether can be used in the formulation of the grease according to the known methods described in the art. In general, the perfluoropolyethers suitable for manufacturing the grease have a kinematic viscosity at 20°C from 20 to 6000, preferably 40 to 3000 and more preferably 500 to 2000 mm²/s (cST). Suitable perfluoropolyethers having neutral (chemically inert) terminal groups are, for example, commercial products such as, for example, Fomblin (R) Y, Fomblin (R) Z (Montedison) and Krytox (R) (Du Pont). Such perfluoropolyethers are described in GB-A- 1 104 482 and US-A-3 665 041, 3 715 378 and 3 242 218. Further perfluoropolyethers are described in EP-A-148 482 (Daikin) and those described in US-A-4 523 039 (Lagow) may also be used. The products known as Fomblin (R) Y comprise oxyfluoroalkylene units and CF₂O, Fomblin (R) Z CF₂CF₂O and CF₂O units, the Krytox (R) products units, Daikin products CF₂CF₂CF₂O units and Lagow products CF₂CF₂O units. Furthermore, mixed perfluoropolyethers constituted by combinations of the above-mentioned units, in particular CF₂CF₂O, CF₂O, can be used. The fluorinated greases based on polytetrafluoroethylene which can be used are those described by J. Messina, J. Am. Soc. Lubr. Eng. (Dec. 1969), 475-481 or in IT-A-963 579. Preferred are fluorinated greases based on polytetrafluoroethylene prepared according to the method disclosed in IT-A-21 590 A/82. Examples of marketed greases which can be used are Fomblin (R) RT, UT 18, OT 20. The layer of grease which is applied is generally in the form of a thin layer. In any case, the washing only has the purpose of removing the thickener contained in the grease since complete removal of the perfluoropolyether which, as is well-known, has a protective effect, is not necessary. It has, furthermore, been found that the residual perfluoropolyether does not lead to any drawbacks as regards the colour and the aesthetic appearance. In general, a perfluorinated or perchlorinated grease is used as solvent to remove the grease. Preferably, commercial products known by the trademark Algofrene (R) , having a boiling point comprised in the range of from 20 to 80°C are used. After the separation of the modelling material, the layer of fluorinated grease may be removed by using a chlorofluorocarbon solvent such as, for example, 1,1,2-trichloro-1,2,2-trifluoroethane, which completely removes the grease without leaving appreciable residual traces. The total removal of the fluorinated grease is evidenced by an I.R. spectrum in which the typical absorption of carbon-fluorine bonds is not present. The following examples merely serve to illustrate the invention and do not limit it in any way. EXAMPLE 1 Two specimens of "Pietra Serena" (sandstone) of 10×10×1 cm are used. On specimen A, without any pre-treatment being carried out, a layer of about 0.5 cm thickness of liquid silicone rubber is spread which, after about 60 minutes, crosslinks to a solid mass. On specimen B, a layer of Fomblin RT 15 (R) grease is uniformly spread in an amount corresponding to 100 g/m². Subsequently, the layer of silicone rubber is spread as on specimen A. After 24 hours, the layers of silicone rubber are removed from the two specimens by tearing. The following results were obtained: SPECIMEN A: The surface shows traces of crosslinked polymeric substance which cannot be removed by the usual solvents for silicone products (ketone-alcohol blends). This material, after having been scraped off and analyzed on I.R. spectrum, showed the typical features of a silicone rubber. SPECIMEN B: The surface has an oily appearance owing to the presence of the fluorinated grease. By wiping with cotton wool soaked with trichlorotrifluoroethylene and subsequently washing by brushing with the same solvent, the components of the fluorinated grease are removed. By evaporation of the solvent used in the prior washing operations, a waxy residue is obtained which, on I.R. spectrum, shows the typical absorption of carbon-fluorine bonds. By scraping the specimen's surface, a powder is obtained which, in its I.R. spectrum, does not show carbon-fluorine bonds. EXAMPLE 2 The tests of example 1 are repeated by using specimens of Carrara statuary marble (white microcrystalline marble). Results are obtained which are similar to those of example 1. EXAMPLE 3 The tests of example 1 are repeated by using specimens of Verona red marble. Results are obtained which are similar to those of example 1.

Claims: Process for the reproduction of works of art in lithoid material, comprising the use of silicone rubbers to obtain a negative mould of the work of art, characterized in that a layer of a fluorinated grease based on polytetrafluoroethylene and on a liquid perfluoropolyether having neutral terminal groups is applied on the work of art before the application of the silicone rubbers. Process according to claim 1, wherein the perfluoropolyether has a kinematic viscosity at 20°C of from 20 to 6000 mm²/s (cst). Process according to claim 1, wherein the perfluoropolyether contains the following perfluorooxyalkylene repeating units: Process according to claim 1, wherein the perfluoropolyether contains repeating units of the CF₂CF₂O and CF₂O type. Process according to claim 1, wherein the perfluoropolyether comprises the repeating units CF₂CF₂CF₂O. Process according to claim 1, wherein the perfluoropolyether comprises the repeating units CF₂CF₂O. Process according to claim 1, wherein the perfluoropolyether comprises the repeating units CF₂CF₂O and and CF₂O.

Inventors: GALLI, GUGLIELMO, PASETTI, ADOLFO
Applicants: AUSIMONT S.P.A.
Application year: 1987
Main classification: B28B7
IPC codes: B28B7, B44F11, B44C3