I've spent the past two or three weeks making masks; also reworking the masks I made in a hurry last summer to have with us on our trip to the Uists. The re-working has consisted mainly of deciding on whether to scrim them or not, and exactly what approach to use in painting the surface.
These two things are related. Scrimming amounts to covering the papier-mache mask with a thin layer of muslin, and we do it to strengthen the mask but also to help protect the paintwork. Paint scratches easily off of raw paper-mache, but clings far better to the cloth of a scrim coating. But scrimming also tends to spoil, to some extent, the modelling on the mask as it fills in detail. So it's always a balance between strength and maintaining the quality of the paint on one hand, and the detail and quality of the modelling on the other. Scrimming is also more likely to spoil a mask that has a lot of fine detail (such as in an old, lined face) than one which has a smoother finish (a child, for example).
So part of the exercise has been finding a way of using paint that works with a partly-scrimmed mask. I've decided on part-scrimming to get the best of both worlds - partly protecting the paintwork and strengthening the mask, but not scrimming the areas of finer detail.
*I seem to be heading towards a painterly finish, which can be seen in the lower photograph. I like painterly masks, and I'm often fascinated to see how alive a mask can be that has been painted with powerful brushwork, contrasts and colours. Many mask makers feel the need to stay close to skin tones and gentle modulations of colour, but my experience is that, especially in the context of stage lighting and backdrops, the painting of a mask can be pushed in surprising ways.