Dissolve a little cosine in ordinary negative varnish, and also a like amount of aurantia in another portion of the varnish. Flow one side of two sheets of glass, one with one varnish and the other with the remainder. When dry bind the two with their varnished surfaces together and you will have an excellent substitute for the expensive and often hard to obtain ruby glass. A pair of glasses so produced is as near safe as one can hope to secure, and passes a very pleasing and comfortable light by which to work. Continued use will result in a slight fading of the color but they are so easily prepared and the fading is so slow, except where sunlight is used as an illuminant, that this is a very slight drawback.