Italian art of the fifteenth century has produced many clay bas-reliefs, apparently from one and the same original and yet presenting slight differences, additions and modifications evidently made after the clay had left the mould but when it was still fresh. This fact has greatly incited the fancy of Italian forgers and largely contributed to the confusion of art critics and the duping of more than one collector. These bas-reliefs represent sacred subjects for the most part, and sometimes it is not merely a question of putting a rose in the Madonna’s hand or a little bird into those of the Infant Jesus, in order to lay claim to due originality, but the modifications are so radical that the whole appearance of the work is changed. It is generally done as follows. A good plaster-mould is made from a good original, and a clay reproduction formed from this mould, which is then modified and changed while still fresh. Should the work to be divested of its original character represent, say, a Madonna and Child, the artist may proceed to alter its size by modifying the border; then, to transform the subject, he may make an addition on one side, of the heads of the ox and ass, taken of course from another original. To change the pose of the Madonna the clay is generally cut behind the head and neck with a fine wire and then the position of the head can be altered at pleasure; from being erect, for instance, it can be inclined, or vice versa. By the same method, and no small amount of skill, arms and hands can be given new attitudes, etc. The final result is a work which passes as an original among foolish art lovers who collect series. _Stucco duro_ imitations are produced by almost identical methods. These compositions are generally made of plaster, which hardens as it dries after being poured into a mould. When the original is to be modified a first model of clay or some other soft modelling material is indispensable, of course, and from this a mould is then taken for the casting of the _stucco duro_. To colour and give a patina either to baked clay or stucco is comparatively easy. The colouring is given with tempera colours, the patina with tinted water, for which tobacco, soot, etc., may be used, applied with smoky and greasy hands. A coat of benzine in which a small quantity of wax has been dissolved is finally laid on with a brush and the whole polished with a brush or wool.