Masks were generally made of linen. Cork and wood were occasionally used.[729] The mask covered the whole of the head, both in front and behind.[730] Caps were often worn underneath, to serve as a protection.[731] The white of the eye was painted on the mask, but the place for the pupil was left hollow, to enable the actor to see.[732] The expression of the tragic mask was gloomy and often fierce; the mouth was opened wide, to give a clear outlet to the actor’s voice. One of the most characteristic features of the tragic mask was the onkos,[733] a cone-shaped prolongation of the upper part of the mask above the forehead, intended to give size and impressiveness to the face, and used where dignity was to be imparted. It varied in size according to the character of the personage. The onkos of the tyrant was especially large; that of women was less than that of men. A character was not necessarily represented by the same mask throughout the piece. The effects of misfortune or of accident had often to be depicted by a fresh mask. For instance, in the Helen of Euripides Helen returns upon the stage with her hair shorn off, and her cheeks pale with weeping. Oedipus, at the end of the Oedipus Tyrannus of Sophocles, is seen with blinded eyes and blood-stained face. In such cases a change of mask must have been necessary. There are a few occasions in the extant tragedies where a change of facial expression seems to be demanded by the circumstances, but was rendered impossible by the mask. Thus in the Electra of Sophocles, the heroine is unable to show her joy at her brother’s return, and the poet has to get over this as best he can. He makes Orestes bid her show no signs of joy for fear of arousing suspicion, while she declares that there is no risk of this, for hatred of her mother has become too engrained in her for her expression to change suddenly, and her joy itself will bring tears and not laughter.[734]