+-------------+---------+----------+----------+-------+-----------+--------+ | | | | Oxide of | | | | | Pottery. | Silica. | Alumina. | Iron. | Lime. | Magnesia. | Water. | +-------------+---------+----------+----------+-------+-----------+--------+ | Roman | 64.00 | 17.77 | 10.23 | 4.86 | .... | 2.23 | | Middle Ages | 72.55 | 20.27 | 2.54 | 1.04 | .... | 3.00 | | Egypt | 81.00 | 13.50 | 1.00 | 3.00 | .... | 1.90 | | Egypt | 92.00 | 4.00 | .... | 2.00 | 0.60 | 0.40 | | Persian | 90.00 | 1.50 | 1.50 | 3.00 | 0.80 | 0.60 | | Jerusalem | 87.16 | 5.50 | .... | 3.00 | 0.78 | .... | | Arabian | 89.95 | 3.87 | .... | 2.00 | 0.51 | 3.00 | +-------------+---------+----------+----------+-------+-----------+--------+ The Egyptian, compounded as above, is that which has been commonly known as Egyptian porcelain. Many of the better known wares of Europe and the East have a common characteristic in the calcareous nature of their pastes. The silica decreases and the lime increases, while carbonic acid appears as a new ingredient. Column headings: S: Silica. A: Alumina. M: Magnesia. I: Oxide of Iron. C: Carbonic Acid. +--------------------+-------+-------+------+------+-------+-------+ | Pottery. | S | A | M | I | C | Lime. | +--------------------+-------+-------+------+------+-------+-------+ | Lucca della Robbia | 49.65 | 15.50 | 0.17 | 3.70 | 8.58 | 22.40 | | Majorca | 48.00 | 17.50 | 1.17 | 3.75 | 9.46 | 20.12 | | Spain (old) | 46.04 | 18.45 | 0.87 | 3.04 | 13.96 | 17.64 | | Valencia (modern) | 51.55 | 20.52 | 1.24 | 2.63 | 10.42 | 13.64 | | Delft | 49.07 | 16.19 | 0.82 | 2.82 | 13.09 | 18.01 | | Persian | 48.54 | 12.05 | 0.30 | 3.14 | 16.72 | 19.25 | | Nevers | 56.49 | 19.22 | 0.71 | 2.12 | 6.50 | 14.96 | | Rouen | 47.96 | 15.02 | 0.44 | 4.07 | 12.27 | 20.24 | +--------------------+-------+-------+------+------+-------+-------+ Of the potteries which hold a place between the hard and soft wares are the Palissy and Henri Deux. The composition of the former is 67.50 silica, 28.51 alumina, 1.52 lime, 2.05 oxide of iron, with a very slight admixture of alkalies. That of the latter is 59.10 silica, and 40.24 alumina. From what has been said, it will be seen that the difference between earthen-ware, stone-ware, and porcelain is to be attributed to a few minor ingredients, to the preparation, and to the degree of heat to which they are subjected. The following table may be studied for the sake of making comparisons: Common earthen-ware Silica, 60; alumina, 30; iron, 7; lime, 2. Blue clay Silica, 46; alumina, 38; iron, 1; lime, 1.