I had all the colours used in oil painting, mentioned in the foregoing list, carefully ground with water, at Mr. Sandys’s, colour-merchant, and from those colours I composed ninety various and sensibly differing tints, for flesh, drapery and landscape; of each tint I had a quantity of a two ounce gallipot full, tempered with water; so I left them well screened from dust till they were become dry again; then I divided each mass of tint in four equal parts; two of each I set by for the comparative use, the other two parts of each I employed in the following manner.
One part of each I tempered again with water, and painted with it over a space of cloth of six inches wide and two inches high, the tints close to each other, in the manner of copper-plate, [page 58], and the cloth waxed as directed Art. IV. [page 26]. The same I did with the entire and unmixed colours.
The other parts of each tint I tempered with the finest nut-oil according to custom, and painted-over with them such another space of six inches by two, as the former, upon oil-cloth. The same I did with the entire colours, and set them by to dry; when dry, I brought the encaustic tints near the fire, and by melting the wax fixed them.
My tints thus ready, I cut each piece of cloth, encaustic and oil-tints, in five equal parts, and disposed of a piece of each in the following manner.
1. One piece of each I exposed in the open air to all the injuries of sun, dew, wind and rain.
2. One piece of each I nailed to a wall in a damp cellar-like room.
3. One piece of each I nailed to the ceiling of a kitchen and near the chimney, where all the year round a fire was kept.
4. One piece of each I nailed to the side of a room I usually inhabited.
5. One piece of each I put between several quires of paper, and confined them in a close drawer deprived of air.
Thus I left them, till the latter end of October, 1759, (the space of twenty-seven months) when I gathered them. Then I took the two parts of tints I had set by and preserved, and tempering the one with water, and the other with oil, painted the first upon a fresh piece of waxed cloth and fixed them, the other tempered with oil, I painted upon a fresh piece of oil-cloth, and after having washed the old tints, on comparing the new and old colours together found as follows.