If you want to restore oil colours that have become dry keep them
soaking in soft soap for a night and, with your finger, mix them up
with the soft soap; then pour them into a cup and wash them with
water, and in this way you can restore colours that have got dry.
But take care that each colour has its own vessel to itself adding
the colour by degrees as you restore it and mind that they are
thoroughly softened, and when you wish to use them for tempera wash
them five and six times with spring water, and leave them to settle;
if the soft soap should be thick with any of the colours pass it
through a filter. [Footnote: The same remark applies to these
sections as to No. 618 and 619.]
633.