I always used butyrate for the whole process, until this year. Then I came across an article on traditional dope finishing. You can find it, I think, on the Randolph website.

Now my process is: nitrate, sand, silkspan, nitrate, nitrate, nitrate with filler (talc), sand, silver butyrate, sand (repeat silver-sand process as many times as you like - it keeps getting better) butyrate colour, clear, clear clear.

Nitrate shrinks better, is easier to sand, and is lighter.

I am buying the nitrate at the local aircraft supply store. I'll probably still buy the colours at the LHS, since you need so little.

The results are well worth the additional effort. And actually it is not much more work, since it dries so quickly, you can do a few coats every day.