Rosin, formerly called colophony or Greek pitch (Pix græca), is a solid form of resin obtained from pines and some other plants, mostly conifers, produced by heating fresh liquid resin to vaporize the volatile liquid terpene components. It is semi-transparent and varies in color from yellow to black. At room temperature rosin is brittle, but it melts at stove-top temperatures. It chiefly consists of different resin acids, especially abietic acid.
I bought my pound of rosin from Brownells 35 years ago and I still have lots... I use it all the time... in the barrel vice and inside scope rings. It cleans off really easy with lacquer thinner.