Although something might be obtained in point of expedition by painting upon a darkish ground, which approaches near the middle tint of your work, yet it is not the best method, as it will greatly tend to corrupt and destroy the purity and fidelity of all your lighter tints, particularly if you do not employ a great body of colour in the laying them in; for though we have some colours which are particularly called transparent, in contradistinction to those which are less so, yet all colours participate of transparency in some degree; and when a light colour, though opaque, is thinly spread over a dark one, it is by the colour underneath rendered dim and muddy. Whereas, on the contrary, the dark colour laid over the light one increases its brilliancy. The best mode of practice, then, is that of employing stiff body colour on a white ground, or on one nearly approaching it, as was the custom of Titian, Rubens, Vandyck, and the other good colourist. From this you work down, proceeding darker and darker, and reserving your transparent colours and darkest touches and tints for the last. By this method, if you do not otherwise prevent it, the effects of time upon your work will be rather for its advantage and its greater brilliancy, than the contrary. However far you may be inclined to advance matters in your bozzo, or fist colouring (and the further you can complete your forms and general effect the better), yet the making out, or rather if I may be allowed the expression, the carving out with your pencil all the detailed particulars, the joints and other knotty parts of the body, according to the happy characteristic delineations of their several forms and perspective aspects, had better, perhaps, be reserved for the second colouring, or repassing over your work, because you will be then freed from many considerations, and the better enabled to attend to those particulars, and execute them at once.