Strong acids and alkalies destroy wool or silk materials. Mild acids,
except nitric, which weakens the material and turns it yellow, are safe
to use. Even mild alkalies such as weak solutions of ammonia water,
borax, or washing soda, must be used with care on wool. Bleaches that
contain chlorine, such as ordinary bleaching powder, also destroy wool
and silk. Sodium perborate is a good bleach to use, particularly on
wool. Use lukewarm water—hot water turns both wool and silk yellow,
shrinks wool, and injures the finish of silk.