27 CFR §21.127

1. (a)Arsenic content. Not more than 1.4 parts per million as determined by the Gutzeit Method (AOAC method 25.020; for incorporation by reference, see § 21.6(c)).
2. (b)Color. White or orange.
3. (c)Rosin content. None when tested by the following method: Add 20 mL of absolute alcohol or glacial acetic acid (m. p. 13° to 15 °C.) to 2 grams of the shellac and thoroughly dissolve. Add 100 mL of petroleum ether and mix thoroughly. Add approximately 2 liters of water and separate a portion of the ether layer (at least 50 mL) and filter if cloudy. Evaporate the petroleum ether and test as follows: Solution A—5 mL of phenol dissolved in 10 mL of carbon tetrachloride. Solution B—1 mL of bromine dissolved in 4 mL of carbon tetrachloride. To the residue obtained above add 2 mL of Solution A and transfer the mixture to a porcelain spot plate, filling one cavity. Immediately fill an adjacent cavity with solution B. Cover the plate with a watch glass and observe any color formation in Solution A. A decided purple or deep indigo blue color is an indication of the presence of rosin.