if possible, because of the reflection. In certain cities the dust is so great that glass must be used on all pictures, while a few old masters and small and finely painted pictures always need the protection afforded by glass. If the glass is to be placed in the frame, however, care should be taken to allow the air to circulate between the painting and the glass, as otherwise the process known as sweating, which is very injurious to the surface of the painting, may take place. In a carefully framed picture where the back is sealed so as to keep the dust from the canvas there should be small holes for ventilation in the side of the frame. These may be covered on the inside with cheese-cloth or stuffed with cotton wool to keep out the dust. If a painting is in a precarious condition it is sometimes put in an air-tight case with glass front. This case is usually made the exact size of the picture and just deep enough to allow for the frame. The glass when placed in this way four or five inches from the face of the picture does not reflect as badly as when close to the painting.
MINOR ARTS
The largest group of material available for exhibition in an art museum and one which in this country is, alas, often neglected is that which
