All the appearances seen in the examination of the stained glass specimens are explainable on the view that some of the glasses are much less durable than others, and have therefore developed the relatively thick corrosion layers which, for the reasons described in the article, have become completely opaque. As well as the approved cleaning with dilute acetic acid, bleaching appeared to render the opaque areas partially translucent. The efflorescence which has appeared on a few of the ground and polished specimens is due to the original altered glass not having been removed. Local grinding and polishing, should clean these surfaces satisfactorily. The use of hydrogen peroxide does not seem to be in any way harmful.