Metal Color is developed in order to be used straight ahead on the airbrush so no thinner needed at all. If someone likes to thinned down with Vallejo Thinner, tap water or alcohol, this can change some properties of the product as bright, light reflected and finish. No Retarder needed or other kind of Vallejo Medium. The Metal Color dries very fast, in an hour you can work over the surface for a weathering process or add more layers for light and shadow effect over a model.

There is a big difference between Metal Color and our regular metallic Model Air colors as Metal Color offers a true metallic aluminum based pigments of last generation and a smooth finish, resistance and great cover answer. The Metal Colors are designed to use for airbrush application direct form the bottle. While thinning is not required, the use of water, alcohol or Vallejo's airbrush thinner can be used to change how the final results look such as color, brightness and overall luster and shine.

Metal Colors can indeed be masked. It is always best to allow the paint to fully cure before any masking. With correct application over a clean surface, with or without primer, the Metal Colors will not lift off the surface after masking.
Brush painting of the Metal Colors is possible. It is best to apply the colors over a primer and depending on the area of coverage will depend on possibly applying a second coat for full coverage. n terms of full brush application on an entire model, the Metal Color range was designed for airbrush application and while these paints self-level to the surfaces really well, the final outcome over large areas may result in some uneven properties in the form of brush marks.
https://youtu.be/Jut0mjzZitQ

You can dowload the metal Color chart here:

http://cdn.acrylicosvallejo.com/a4ba8f8b0405f2b1e4d78e8500b83692/CC069-MetalColor-rev00.pdf