One more factor that affects the quality of sound of a voice and the articulation is the mouth. The singer has to learn how to articulate properly and to be able to produce a homogeneous sound (read more at the article about the sound). 
This is a goal that can be succeeded with the collaboration of the three elements Breathing - Mouth - Mask. 
In this occasion, the mouth is the main element for the attainment of good articulation, of volume and of the homogeneity of sound, with the contribution of the mask, which will be analyzed in the next article.

It is very important that the singer studies articulation in front of a mirror, where he/she will be able to observe, control and manage the opening and shaping of his/her mouth accordingly. Vowels should be pronounced clearly, thus the mouth (along with all the other muscles, "working" together) should be flexible, free, "expressive" and also relaxed. The next step for achieving the "clear" vowel and the "rounded" sound is the creation of the called "dome" in the oropharyngeal cavity. This can be achieved by understanding the sensation of lifting the soft palate, therefore watching the uvula going up.

This "dome" constitutes an opening, an expansion of the space inside the oropharyngeal cavity and it is the factor that gives "volume" and enriches the voice with harmonic frequencies.

All the above, with the simultaneous operation of the support of diaphragmatic breathing (read more at the article about breathing) and the targeting of the sound towards the mask (for which there will be an extended analysis at the next article), show us the right direction for mastering homogeneity, volume and dynamics in our vocal instrument.