Hey there Luis,

I haven't been, and don't have a problem. I think if you were using a more metallic type of paint like say the liquid gold series I would say yes, but I don't find that the normal Vallejo Metallics are hard to clean out of the brushes, they behave the same as any other Vallejo paint.

That being said, I find that the metallics in the Vallejo Model Air range are a better metallic. Not so much for the copper and gold, but your aluminum, silver, gunmetal etc. they seem to be a bit better. And even though they are in the Model Air line, they still brush paint very well and usually in one coat as they are just a hair thicker I find than the other Air colors.

Also, something to keep in mind, Vallejo # 521 Metal Medium is just that...a metal medium. You can take it and mix it with any other Vallejo color to turn it into a metallic. Fancy a Metallic Russian Green T34.....we can do that!