BUILDING AND ORNAMENTAL STONES OF N.S.W. 183 



colouration from cement or other foreign substances, or from 

 climatic conditions, for the granites of the Post Office colon- 

 nade show no sign of changing colour after a thirty years' 

 exposure, and the Montague Island bases of the columns, 

 with their labradorite crystals are resisting the inroads of 

 climatic conditions very satisfactorily. Such constancy 

 of colour however, does not hold with sedimentary and 

 metamorphosed rocks, for sandstones are generally a darker 

 shade when first quarried and become lighter in colour, or 

 vice versa when exposed. For instance the mountain 

 sandstone is very soft when first quarried but on exposure 

 hardens and changes to almost white; and even the Pyrmont 

 sandstone upon exposure changes to a very pleasing straw 

 colour. In the fire test (infra) Sydney sandstone changes 

 to light brick red, due no doubt to the presence of oxide 

 of iron, a constituent that in all probability gives the dark 

 brown colour to the Ravensfield sandstone. 



In the case of marbles colour plays a very important 

 part and requires special care and attention, for the market 

 value of a stone is often influenced by its colour without 

 regard to its strength and durability, and now that so many 

 varieties are being submitted to the architectural world of 

 New South Wales, it is hoped that a gratifying, artistic 

 and harmonious combination of stone colours will result. 

 We have used the word harmonious because a building of 

 many colours is not art, but at the same time a too sombre 

 colour is not desirable in this climate of blue sky, for to 

 our taste the new railway station in its internal mural 

 colours is rather inclined to the dull side of things. 



The colour of a sandstone rock when freshly quarried 

 may be pale coloured or almost perfectly white, but after 

 a short time of exposure the colour may change to a buff 

 or the stone may be streaked with irregular patches of 

 ferrous oxide. Such discoloration depends chiefly upon the 



