Winsor & Newton Professional Acrylic Medium, White Gesso, 225ml (7.6-oz)

Q: Has anyone tried this as a photo transfer to wood? Using regular acrylic medium now, but don't like the white base.

This might work because it is clear and flexible when dry. I have used it on wood before and it is perfect.

Q: Safe to use as a sealant for acrylic paint repainted barbie/doll faces? (vinyl&plastics)? water-based/mixable? does it dry sticky? any fumes?

I've used the Winsor & Newton Matte Acrylic Varnish as a top coat and protective finish whenever a colored acrylic is used as a base. I've used W&N varnish over acrylic primers and paint on hard plastics, wood, and metal surfaces. The underlying acrylics from any company can be used as a base as long as they are labeled as such. In answer to your specific questions - I've never painted on vinyl or soft plastics like doll faces but if your acrylic base coat and color adheres well to such surfaces then the W&N varnish will also adhere. The varnish is only a top layer that locks onto the underlying coat of paint to prevent smudges and to keep the surface clean. And of course the UV with this varnish is supposed to protect against sunlight discoloration - but be aware no UV coating will last forever. Acrylics by definition are water based. Although I might thin color acrylics with water I would not thin any varnish with water because it would affect its chemical makeup and thus its functionality. W&N does sell an acrylic based thinner though that I always use when airbrushing since the varnish is a little thick for that purpose. I imagine that this thinner will also work when hand brushing if that is what you're doing. The varnish dries hard and there is a mild smell to the liquid varnish but not an unpleasant one. That smell disappears once the varnish has dried.