Yep, allow the base coats to dry fully, paint, inks, washes will all have the effect. Yep mix it well, very well. Another trick is to pre-heat the figures on a radiator before doing it, not hot just warm, it dries them out and gets the temp right for matte. This works really well for spray mattes too.
As for saving it... not managed that yet, had to strip or touch in.