The silica has at all times been derived either from solid quartz, whether in the form of rock crystal or of the white pebbles from the beds of Alpine rivers, or more often from sand obtained either by excavation or from the seashore. In the case of the alkali, the maritime people of the South extracted their soda, for the most part, from the ashes of certain plants growing in salt marshes near the sea. Most of these maritime plants belong to the natural order of the Chenopodiaceæ, the goose-foot or spinach tribe, and we find among them various species of Salsola, Chenopodium, Salicornia, etc. These plants were all included in old days under the vague name of _kali_. The roughly lixiviated ashes exported from Spain were known in the trade as _barilla_; those from the Levant as _roquetta_.[4] In other instances the impure alkaline carbonates were found ready at hand—as in the case of the natron deposits not far from Cairo. In the North the principal source of soda was till recent days the _varech_ or kelp, cast up on the west coast of France and of Scotland. The inland folk, on the other hand, had to find the alkali for their glass in the ashes of plants. This ‘potash’ was obtained by lixiviating the ashes of various trees and bushes—in Germany the ashes of beechwood, in France those of the bracken or _fougère_, were most in favour. The quality of the glass depended in great measure upon the care taken in the preparation of the soda or potash. But the more impure ashes had this advantage: the amount of lime, to say nothing of the iron oxide and alumina, that they contained, rendered unnecessary in many cases the addition of any further basic material; even the comparatively pure Spanish barilla contained as much as seven per cent. of lime. In other cases that base had to be added, generally in the form of a more or less impure limestone. Of the furnaces and of the various operations that come into play in the preparation of the glass I shall treat as the occasion arises in the following chapters. As, however, in this book we are—at least after the ‘primitive glass’ has been dealt with in the next chapter—almost exclusively concerned with vessels of ‘hollow ware’ made by a blowing process, it may be well to indicate, in this introductory chapter, the nature of this process, and to give the names of the principal tools used. These implements—apart from quite modern improvements with which I am not concerned here—are of the simplest nature, and have undergone little change during the last five hundred years—perhaps I might say since the days of the Romans.