Differences in series of paint brands

[Amanda Grosjean]

I am about to make the big switch from buying my paints at the local craft store (subject to being at the mercy of them being out of certain colors or a higher series) to purchasing them solely online. I am not going to ask what your favorite brand is, it has been answered many times before in various threads and seems to be a very personal thing, mostly what you were introduced to as a young artist and what you become used to. I'd be very impressed if there is anyone out there who has tried every single brand in this catalog.

My question is actually about the "series" of these paints. Your options are very limited locally at the stores but now I have the option of picking series 1-6 of each color. Obviously there is a significant difference in price but, chemically...and from a usability standpoint, what makes them superior as the series goes up? How does a series 4 from Sennelier compare to a series 4 from say Winsor Newton? Perhaps the Sennelier is more but is that reflective of the quality or that maybe one is from another country, tacking on extra money. Does anyone here actually purchase the series 6, 80 dollar and up, 40 ml tube? It is certainly not something I could afford but ..is it worth it? Also, has anyone ever had problems mixing 2 different brands?

-Amanda