1842.] 



THE CIVIL ENGINEER AND ARCHITECT'S JOURNAL. 



353 



of tlie pit. Tlio air-pump buckets of steam engines, in which the body was 

 of cast iron and the valves of gun-metal, formed the most perfect kind of 

 galvanic apparatus ; they should be made entirely of gun-metal. In manu- 

 factories of vinegar and pyroligiieous acid the decay of cast iron was very 

 rapid. 



Mr. Glynn attributed in a great degree the rapid decay of cast iron in coal 

 mines to the presence of sulphuric acid evolved from the pyrites. Mr. Philip 

 Taylor agreed with Mr. Glynn; even copper pipes were rapidly destroyed in 

 the bilge water of vessels, which always contained much sulphuretted hydro- 

 gen — he recommended the use of stout lead pipes in such situations ; they 

 would be found much more durable. 



Mr. Davidson had found it necessary to substitute gun-metal gratings for 

 the cast iron ones at Messrs. Hanbury's brewery, as althongh they were f in. 

 thick, they bad been entirely destroyed in four years. 



The President gave a short account of the construction of a light-house 

 now making by Messrs. Gordon & Co. at Deptford under his directions for 

 the Point of Air. The lanthorn for it would be cast from a gun which had 

 been raised from the wreck of the Royal George. 



Sight-tube for Marine Boilers. 



Mr. C. W. Williams exhibited and explained the sight-tubes which he now 

 used for the marine boilers of the City of Dublin Steam Packet Companv's 

 vessels. • 



The instrument consists of a wrought iron welded tube 2 inches diameter 

 with a screw thread cut upon the exterior; it is inserted across the wafer 

 spaces of the boilers, and secured by means of nuts in such positions behind 

 and opposite the furuace, as enables the engineer to see all that goes on 

 intenorily, particularly the degree of perfection or imperfection in which the 

 gaseous matter enters into combustion, and the effect of admitting or ex- 

 cluding the air. 



The instrument had been found very useful, not onlv in experiments, but 

 in practice on the large scale, and he deposited it in the Gallery of the Insti- 

 tution in order that it might serve as a model for those who were inclined to 

 adopt it in marine boilers. 



THE VARIATION OF THE COMPASS. 



Observations made at the Royal Observatory, Greenwich, 



G. B. Airy, Astronomer Royal. 



During the month of June, 1842, the dipping needle n as out of repair. 

 REPORT OF THE COMMISSIONERS ON THE FINE ARTS. 



(Continued from page 308.^ 



VARIOUS COMMUNICATIONS ON FRESCO PAINTING. 



The follow ing papers contain further information respecting the practice of 

 fresco-painting, or point out the sources where the subject is more fully 

 treated. In inserting these communications and extracts, it has not been 

 possible to avoid occasional repetition, but in some cases coincident testimony 

 may be necessary to establish or recommend particular methods. While the 

 qnesfion respecting the adoption of fresco remains, for the reasons before 

 stated, undecided, it may appear premature to describe its methods so fully, 

 but it IS precisely because so little is generally known of the process, in this 

 country, that it has been thought desirable to take this means of putting the 

 artists and the public in possession of the information that has been col- 

 lected. 



A communication on fresco by Professor Hess, of Munich, (to Mr. William 

 Thomas) need not be given at length, as it agrees generally with the fore- 

 gomg statements by Director Cornelius. In speaking of the preparation of 

 the wall Professor Hess recommends " bricks well dried, and of equal hard- 

 ness" as the groundwork of the mortar and plaster. Jlr. Thomas observes, 

 " all the frescos in Munich are painted on the (plastered) brick wall : laths 

 with wattling and copper nails are not approved of, as the risk of bulging is 

 thus increased. The use of lafhs is sometimes necessary for certain surfaces, 

 but the professors in Munich are decided that a brick ground is to be pre- 

 ferred wherever it is practicable, not only on account of its soUdity, but also 

 because it is better adapted for the execution of the painting. The brick 

 ground absorbs superfluous water and k-eeps the plaster longer in a fit state 

 for painting upon. The painting ground dries much quicker on laths as two 

 surfaces are presented for evaporation. The walls ought to be thoroughly 

 dry. A wall of a brick, or a brick ai.d a half, in thickness, is preferable to 

 paint upon. Professor Hess once observed to me that where the walls in the 

 lower portions of buildings were five or six feet thick, the liability of saline 



ick 



matter making its appearance was much increased, as the mass of wall remains 

 onger i n a humid state." 



Mr. C. H. Wilson, professor of ornamental design in the Royal Edinburgh 

 Institution, has contributed much useful information on the subject of fresco 

 derived from his own observation in Italy, and from recent communications 

 from his father Mr. Andrew Wilson, now at Genoa. He observes : " In Italy 

 the practice of lathing walls is unknown, but many of the finest Italian ceiL 

 mg frescos are on lath, and are in perfect condition. Most vaulted ceilines 

 in what IS termed the „iano nobile, or principal floor of every pilace, are con- 

 structed of wood. The lathing in this case is not attached to single thiu 

 pieces of timber, cut to the shape of the ceiling, but to a strong gratin- ■ 

 some cases the ribs and transverse pieces of this grating are four inches "th 

 each way. The lathing in Italy is a very peculiar process. The material is 

 the reed, which is cultivated so exfensivelv in that country, and used in so 

 inany ways. It grows to the length of about 18 feet, and is rather more 

 than one inch and a quarter diameter at the base. When these reeds are 

 used for lathing they are split, and not being strong enough for the purpose 

 in this state, they are wattled upon the grating. The result of this somewhat 

 complicated contrivance is a framework of great strength." 



Mr. Hamilton, a distinguished architect of Edinburgh, observes- "In the 

 preparation of walls and ceilings for fresco-painting, no expense should be 

 spared ; battens and lath are obviously perishable materials, and therefore 

 ought to be avoided. The damp from exterior stone walls may be guarded 

 against by lining them with brick, and now ihat the use of cast-iron is so well 

 understood, the girders or joisting of houses where fresco-painting is con- 

 templated should be of iron arched with brick between, and thus a perfectly 

 level ceiling may be formed of the most durable kind." For the more effectual 

 prevention of damp, Mr. Hamilton recommends that the lining of brick should 

 be somewhat detached, leaving a small space between it, and the stone wa'I, 

 to which it could be bound at intervals. Mr. C. Wilson in communicating 

 this opmion, remarks, that as the brick lining, added to walls of sufficient 

 solidity for the support of the ceiling here described, would diminish the size 

 of the rooms, tiles placed edgewise might be used instead of bricks. These 

 should, however, be of sufiicient strength to be in no danger of fracture from 

 any ordinary accident. To guard against damp from roofs or even occasional 

 washing of upper floors, it is also suggested that a coating of asphalte might 

 be applied on the upper sides of the arches of the ceiling. In some cases 

 asphalte might be necessary in walls: Mr. C. Wilson observes, that a French 

 architect, M. Polonceau, eftectnally checked the progress of damp from a 

 humid soil in several instances, by covering the horizontal surface of the 

 masonry a few inches above the level of the soil with a coating of liquid 

 asphalte, applied with a brush ; when this w.as drv it was covered with a 

 layer of coarse dry sand, and the building then proceeded. An external joint 

 of hard asphalte at the same level is necessary eftectuallv to cut off all com- 

 munication of damp. (See the " Revue Generale de I'Architecture, September, 

 1841). These and other remarks on the construction of walls and ceilings 

 have been communicated with all deference to the judgment and experience 

 of the architect of the new buildings at Westminster. 



In considering the question respecting the comparative fitness of laths and 

 bricks, as a groundwork for fresco, it is not to be forgotten that the battened 

 wall sooner adaps itself to the temperature of the atmosphere, and is there- 

 fore less likely to be aflected by external damp ; while the coldness of the 

 more solid wall causes the rapid condensation of moisture in humid weather. 

 This evil might perhaps be guarded against by due precautions with rcard 

 to temperature and ventilation. ° 



Mr. C. Wilson next describes the mode of preparing the lime at Genoa: — 

 " The lime having been slaked is mixed in a trough about six feet in length, 

 and 20 inches in width ; at the bottom it is somewhat narrower. The in- 

 strument used in mixing it is similar to that used by our masons. The lime 

 is worked with this, and water is thrown in till the substance is of the con- 

 sistence of cream. At the end of the trough there is a little sluice, the open- 

 ing of which however comes only to within an inch and half of the bottom 

 of the trough. On being drawn up, the sluice allows the lime to escape, but 

 small stones or impurities which may have sunk to the bottom are prevented 

 from passing by the ledge under the opening. The lime is received in a 

 pit dug in the mere earth (not hned) to the depth of several feet, and of any- 

 convenient size. The process of mixing in the trough is repeated till the pit 

 is well filled, the trough being washed out with clean water every third or 

 fourth mixing." 



" The lime being thus prepared is left in the pit from eight to Iwetoe 

 months* according to its ascertained strength. The lime for the first rough 

 coat need not be kept more than two months : this is allowed to drv per- 

 fectly, before the next coats are put on. The proportion of sand to lime is 

 the same as with us, viz. two of sand and one of lime. No hair is used by 

 the Italian plasterers. The lime of which the inlonaco or coat of fine plaster 

 is composed, is however to be subjected to a much more careful jircparation 

 than that used for the first coat. .Uter it has been kept the requisite time, 

 it is taken out with a spade, the greatest care being necessary not to come 

 too near the edges, sides, or bottom of the pit, lest any clay or earth should 

 be taken up with the lime. It is now thrown again into the troughs, and is 

 again thoroughly mixed with water, till it is not thicker than milk ; it is thea 

 allowed to escape us before through the opened sluice, but this time it passes 



In Florence, where fresco-painting is now occasionally practised, artist 

 are of opinion that. •' the lime slrould be kept in the moist state from .ie/i 



kept . 



(0 tweh'e months, olliernise ii will burn both colours and brushes. 



3 D 



