Mixture of Orpiment and _Viride AEris_ in a due Proportion, the
Mixture lost its purple Tincture, and became perfectly dun. But the
Experiment succeeded best without Minium thus. To Orpiment I added by
little and little a certain full bright purple, which Painters use,
until the Orpiment ceased to be yellow, and became of a pale red. Then I
diluted that red by adding a little _Viride AEris_, and a little more
blue Bise than _Viride AEris_, until it became of such a grey or pale
white, as verged to no one of the Colours more than to another. For thus
it became of a Colour equal in Whiteness to that of Ashes, or of Wood
newly cut, or of a Man's Skin. The Orpiment reflected more Light than
did any other of the Powders, and therefore conduced more to the
Whiteness of the compounded Colour than they. To assign the Proportions
accurately may be difficult, by reason of the different Goodness of
Powders of the same kind. Accordingly, as the Colour of any Powder is
more or less full and luminous, it ought to be used in a less or greater
Proportion.

Now, considering that these grey and dun Colours may be also produced by
mixing Whites and Blacks, and by consequence differ from perfect Whites,
not in Species of Colours, but only in degree of Luminousness, it is
manifest that there is nothing more requisite to make them perfectly
white than to increase their Light sufficiently; and, on the contrary,
if by increasing their Light they can be brought to perfect Whiteness,
it will thence also follow, that they are of the same Species of Colour
with the best Whites, and differ from them only in the Quantity of
Light. And this I tried as follows. I took the third of the
above-mention'd grey Mixtures, (that which was compounded of Orpiment,
Purple, Bise, and _Viride AEris_) and rubbed it thickly upon the Floor of
my Chamber, where the Sun shone upon it through the opened Casement; and
by it, in the shadow, I laid a Piece of white Paper of the same Bigness.
Then going from them to the distance of 12 or 18 Feet, so that I could
not discern the Unevenness of the Surface of the Powder, nor the little
Shadows let fall from the gritty Particles thereof; the Powder appeared
intensely white, so as to transcend even the Paper it self in Whiteness,
especially if the Paper were a little shaded from the Light of the
Clouds, and then the Paper compared with the Powder appeared of such a
grey Colour as the Powder had done before. But by laying the Pape