Joseph Shore On Singing in the mask

What is it? Is there anything to it? Popularized by Jean De Reszke at the turn of the 20th century.

William Johnstone-Douglas, De Reszke's assistant for many years, writes: "He (De Reszke) placed great importance on mask resonance, which was used to obtain maximum resonance and ring in the voice. This was gained by allowing just enough room for the tone to be thrown up into the resonance spaces behind the nose, using the sound of the French 'an',(a~) in 'souffrance'. I gather that he was obtaining a vibration of air in the upper turbinate of each nostril, which lies almost between the eyes. DeReszke’s mask resonance was simple nasality as Johnstone-Douglas' account of his teaching shows:
" Because of its numerous nasal syllables, a very effective sentence to obtain this resonance was 'Pendant que 1'enfant mange son pain, le chien tremble dans le buisson,' monotoned on each successive syllable of the scale...In a course of purely mask singing 'o' and "a" would become 'on' and 'an,'(i.e. nasalized), the open 'e as in "etre became 'ain'..."
This is a simple account of nasalizing vowels, nothing more.