The silica for this glass was derived, as we have seen, from quartz pebbles, but we have no information as to the source of the other important constituent, the alkali. It is known, however, that the glass of the ancients was essentially a soda-glass, made for the most part in maritime regions. Again, the possibility of obtaining an abundant supply of fuel has always been an important element in the selection of localities for glass-works. Now in the neighbourhood of Thebes fuel must always have been scarce and dear, and it is uncertain whether there was any source of soda near at hand. We may perhaps regard the glass-works of Tell-el-Amarna as due in the main to the caprice of that eccentric sovereign Akhenaten. They were probably started at his orders to supply the demand for the new material then coming into favour at his court. In so far as the making of glass ever became an industry in Egypt, we must look rather to the neighbourhood of the Delta for its development. There at least fuel would be more abundant, and there a supply of soda was at hand in the ashes of marine plants, even if the natron of the adjacent salt lakes was not yet used for the purpose.[10] But until a much later date, glass was always a somewhat rare substance in Egypt, and was, it would seem, never produced on a large scale. I must now say something as to the source of the colours with which the Egyptians stained their glass. In the absence of any satisfactory analyses, we are strangely in the dark on this interesting question.[11] But everything points to the predominance of copper as a colouring material at an early period, so much so that we may perhaps consider—and this is a suggestion that has indeed been already made by a French writer—that the invention of glazes in the first place, and then that of glass, were offshoots of the metallurgy of copper, and that these industries may therefore be especially connected with the copper age. In any case, it was in all probability not, as in later days, a more or less transparent and colourless glass, but rather one of a pale or dark blue colour, that at the commencement formed the basis to which a decoration of other colours was added.