Soft Mixing White - Oil Colour.

What sort of emulsion? Safe whites to use for underpainting are Underpainting White, Foundation White, and thinned down lead white. Or don't use any white at all, of course. Or for the underpainting, not so much for just blocking in, Alkyd white (eg, Griffin alkyd). It's difficult to avoid all white in the underpainting process if you use a tinted canvas - I usually get round the use of it altogether by using the initial laying-in as my equivalent of laying down an Imprimatura, but there are other ways of doing this. Tom Keating's videos are still available on YouTube and offer a variety of alternatives, including tempera. If the initial coloured wash is fairly light, on the other hand, you can draw into it with much darker paint then go straight in with full-strength white and the basic colours you'll be using for the final assault. Soft mixing white isn't an underpainting white, but heavily thinned down with turps it should be all right. The idea of it is to extend colour without reducing it too much - to blend colours together without making them too pastel in tone, but then, a version of it is made by more than one manufacturer, and each one varies. I don't know who this leading artist is of whom you speak, or would study their individual method further: I think my suggestion to him or her might be that there's such a thing as being in too much of a hurry.

Winsor and Newton still do an Underpainting White, I think. Foundation White is, possibly was, largely lead chromate. I will investigate and, like General MacArthur, or Fu Manchu, return. Always avoid B & Q, other than for hardboard off-cuts.... In passing, I have a longstanding prejudice against Ken Howard but will try to approach his methods objectively. (I like to drop these trails - who knows where they might lead?)

Sigh - they do make things damn' difficult. It seems that Winsor and Newton have stopped making underpainting whites, Daler Rowney haven't made them for years, and even Michael Harding doesn't seem to have a specific underpainting white. You might try W & N's Flake White Hue, or Gamblin's Flake White Replacement, and thin them down substantially with turps. I shall keep looking in the meantime, and hope to find something - (although I'd still have a go with Alkyd Titantium White, in your place). Cremnitz White is available from Harding, but at £56 for a large canister I wouldn't want to use it for underpainting, even if it's stringy consistency didn't make it unsuitable anyway. This wouldn't be a problem if it weren't for a) ninnying regulations about lead, b) the closure of just about all lead-producing facilities in Europe. But there it is: at least there are some alternatives. W & N do a transparent white, I see, as well: I haven't tried it, and it may not be what you're after anyway. It would presumably have some of the qualities of Zinc, though, which I know you use, much thinned down (as it certainly would need to be). Should I find anything else, I'll post it.

http://www.gamblincolors.com/artists.grade.oils/whites/ Available from Jackson's Art Supplies. Robert Gamblin recommends his Flake White Replacement for underpainting, but also offers several others.

Alkyd - it's an oil paint mixed with an alkyd resin, no water involved. If you look up Griffin Alkyd paints, made by Winsor and Newton, you'll find a range of quick-drying oils mixed with this resin, which are fine for use under regular oils, or in their own right - ie, you can start and finish a painting with them - but don't paint with them over regular oils because there's a danger of cracking.