1907.] on Conservation of Hisiork Buildings and Frescoes. 60B 



layintr down a rule it may be said that where so much as 2 per cent, 

 of this sulphate is present, baryta treatment is indicated. 



In the case of the Cliapter House, AVestminster, to which I would 

 now direct your attention, the proportion of calcium sulphate was 

 far more than enough to fulfil this condition of success. Although 

 the exterior of this building, and most of the upper portions of the 

 interior, date only from the time of the restoration carried out by 

 Sir Gilbert Scott, much of the original work of the middle of the 

 thirteenth century remains. The Chapter House is in the custody 

 of H.M. Office of Works. The successive First Commissioners, as 

 well as the permanent officers of that Board, have sympathetically 

 regarded its preservation. So when, in 1900, Mr. Micklethwaite 

 pointed out to Mr. Akers Douglas that serious tokens of disin- 

 tegration were appearing in the early mouldings of the arcading, 

 in the diaper work above, and in the exquisite sculpture of the 

 soffits of the entrance arch, my advice was asked. A few experi- 

 ments showed that the disintegration and efflorescence were due to 

 the formation of gypsum, which, in some parts of the decayed 

 material, exceeded 17 per cent.* The stone, a sandstone, with 

 a calcareous cement, and known as firestone and Reigate stone, 

 no longer contained any calcium carbonate — indeed, had an acid 

 reaction, and yielded to water 4 per cent, of saline matter other 

 than gypsum. You will recollect that the conversion of calcium 

 carbonate into gypsum is not only accompanied by the evolution of 

 much carbon dioxide, but that loO volumes of the former compound 

 expand into 120 volumes of the latter. The rationale of the baryta 

 treatment, to which the interior stone- work of the Chapter House 

 was submitted, has been already described ; but it may be added 

 that the operations were commenced in May 1900, continued in 

 1901, and completed in 190:). Before treatment, a touch of the 

 finger sufficed to bring away the surface of the carving, afterwards 

 the stone .was as sound as that newly quarried, and harder. Inci- 

 dentally it was found that decayed Purbeck marble was equally 

 amenable to treatment ; a column at the right hand wall of the 

 entry having been successfully barytised. In no instance has there 

 been a sign of subsequent deterioration. Full particulars are to be 

 found (of the operations in the Chapter House) in the Parliamentary 

 Paper, Cd. 1899/1904. It may be of interest to mention that 

 220 gallons of baryta- water sufficed to treat 560 superficial yards in 

 the Chapter House and its inner entry, eight applications being 



From the Chapter-House. 



. none. 



. 17-85 per cent. 



•37 



•05 

 . acid. 



