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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interfere with the softness and delicacy of colouring required in this
subject.
The centre will be sound to be the darkest colour, and may be tinted
' J
with a strong tint of carmine. The unfolded petals may be shaded
with a thin tint of crimson lake. It will then be advisable to proceed
with the outer circle of petals, making the broad touch os carmine at
the bottom of the leaf, and softening it off towards the edge, taking
care to keep them nearly white on the side on which the light strikes,
and to let a broad tint pass over those petals that are in shade, as that
will form the middle tint to them. When the next tint is applied,
proceed in this way till the colour joins the centre, then return to the
outer circle again, rub up a rather stronger tint os carmine, and give a
broad touch over the darkest part of the first tint, and with a clean
brush draw the colour while wet in streaks over the lightest part os
the petals. The brush must have but little water in it, or it will cause
the colour to run and spoil the tint. The same means must be used on
the dark side, only the tint may be used stronger, and the marking
more broad. Take great care to form the white edges os the petals
with the dark masses of the carmine, and that the sostening os the
latter colour does not come near them. When all the petals are
formed, the light veining maybe sormed with a sine pencil, dipped into
a faint tint of lake.

Nothing can be more beautisul or more easy than this subject is the
painter proceeds with patience and regularity, but any thing like haste