This earliest civilization was completely master of the arts of combined labour, of masonry, of sculpture, of metal-working, of turning, of carpentry, of pottery, of weaving, of dyeing, and other elements of a highly organized social life; and in some respects their work is quite the equal of any that has been done by mankind in later ages. Though simple, it is of extreme ability; and it is only in resources, and not in skill, that it has ever been surpassed. Certain products were then scarcely if at all known, and it is in the application of these that the civilization of later times shows a difference. No metal was used except copper, and hence flint was largely needed. And glass was probably unknown, although glazes were in use. But in most other respects the changes of later times are rather due to economy of production, and an increased demand for cheap imitations. The work of the great period of the twelfth dynasty differs mainly in the freer use of writing, the greater quantity and poorer quality of the sculptures or paintings, and the introduction of glass and of glassy frits for colouring. The next great period, the eighteenth to the nineteenth dynasty, is marked by the use of bronze, and the disappearance of flint tools. The art of glazing was much developed, and attained a brilliancy and variety of colouring, and a boldness of design, which was never again reached, unless perhaps by the mediaeval Orientals. But artistically the finest work of this age scarcely reaches the perfection of the sculpture and drawing which had already passed away. The next serious change was the introduction of iron, of which there is no satisfactory evidence until about 800 B.C. Iron may have been known perhaps as a curiosity, just as one example of bronze occurs two thousand years before it came into actual use; but it had no effect on the arts. And shortly after came the Egyptian renascence, when the cycle of invention was run through, and the Egyptians were reduced to copying slavishly, and without the original spirit, the works of their ancestors. The Western influence became predominant, and importations instead of development govern the succeeding changes.