Whittock, Nathaniel: The Art Of Drawing And Colouring From Nature, Flowers, Fruit, And Shells: To Which Is Added, Correct Directions For Preparing The Most Brilliant Colours For Painting On Velvet, With The Mode Of Using Them, Also The New Method Of Oriental Tinting ; With Plain And Coloured Drawings (London, 1829)

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for instance, in this group, there is a beautisul bloom upon them, as
though they were just gathered. This appearance can only be seen
in the original picture, as it is impossible to colour prints with this
degree os persection. This, is done with the point os the brush, would
be more troublesome than stippling the human sace on ivory, as many
who have attempted it have sound, but is produced in a moment by
those that are acquainted with the method. The dark parts os the
grapes are heightened by being varnished with thin gum water. When
this is done in every part, and got quite dry, a little finely powdered
smalt is put in a small muslin bag, and, by breathing on the drawing,
the parts varnished with gum water will become damp: then, by
shaking the smalt through the muslin upon it, the small particles os
blue will adhere, and give the bloom with better effect than by the
most laborious painting. The bloom upon plums, or any other sruit
requiring it, can be produced by the same method. The sursace of
peaches, apricots, and other kinds os wall sruit, is soft and downy.
This effect can be produced in water colours, by wetting the mass os
colour with clean water, and brushing it with a dry camel-hair pencil;
this will drag up the colour, and give the roughness required. Care
has been used in the selection os this group, to make it a fit example
sor any kind os painting contained in this work.