Could it not be executed on a marble ground that has been sifted on a distemper or size preparation to avoid the hability of turning yellow which it does when an oil ground is used – The painting to be executed partly with powder colours and partly with crayons – zinc white to be used in both cases then, might it not be fixed by sprinkling with very weak collodion instead of using the ordinary spts. wine & mastic solution wich darkens the tints a little, which I expect that collodion would not as it is not of an oily or resinous nature but deposits only a transparent cotton fibre. …. Al.. the soft wash might be so done and fixed & then if the picture might have its finer lines & tints put on with ordinary watercolour for the size ground would be rendered impervious by the coating of collodion which would have fixed it.,