This was simply pure _lime-white_, made by burning the finest white marble; the lime was then washed in abundance of pure water, then very fine ground and finally dried in cakes of a convenient size; see Cennino Cennini, § 58; and Theophilus, I. 19. The medium used with it was the purest size or gum Arabic of the most colourless kind. Another white pigment was made of powdered chalk and finely ground egg-shells; this was a less cold white than the bianco di San Giovanni. _White lead._ _White lead_ (_cerusa_ or _biacca_) was also used[279], especially by the later illuminators, but with very unfortunate results, since white lead is liable to turn to a metallic grey or even black if exposed to any impure sulphurous atmosphere. Many beautiful manuscripts have suffered much owing to the blackening of their high lights which had been touched in with white lead; especially manuscripts exposed to the gas- and smoke-poisoned air of London or other large cities. _Process of manufacture._ The _biacca_ of the mediaeval illuminator was made in exactly the same way that Vitruvius and Pliny describe; see Vitr. VII. xii.; and Pliny, _Hist. Nat._ XXXIV. 175. A roll of lead was placed in a clay _dolium_ or big vase, which had a little vinegar at the bottom. The top was then luted down, and the jar was left in a warm place for a week or so, till the fumes of the acetic acid had converted the surface of the lead into a crust of carbonate. This carbonate of lead was then flaked off and purified by repeated grinding and washing. In order to keep the white pigments perfectly pure, some illuminators used to keep them under water, so that no dust could reach them. _Black inks._ Two inks of quite different kinds were used for the ordinary text of mediaeval manuscripts. _Carbon ink._ One of these was a pure carbon-black (modern Indian or Chinese ink); this has been described under the classical name _atramentum librarium_[280]; see above, page 27. The great advantage of this carbon ink is that it never fades; it is not a _dye_ or _stain_, but it consists of very minute particles of carbon which rest on the surface of the vellum. _Iron ink._ The other variety was like modern black writing ink, only of very superior quality. This acts as a dye, staining the vellum a little below the surface. Unfortunately it is liable to fade, though when kept from the light (as in most manuscripts) it has stood the test of time very well. Sometimes the mediaeval illuminators distinguished these two kinds of black ink, calling the first _atramentum_ and the second _encaustum_; but frequently the names are used indifferently for either: see Theophilus, I. 40. The _encaustum_ was made by boiling oak-bark or gall-nuts, which are rich in tannin, in acid wine with some iron filings or vitriol (sulphate of iron). The combination of the iron and the tannin gives the inky black[281]. Both these black inks were used with gum Arabic. _Beauty of the plain text._