What is "to tone up"

Tone \Tone\, v. t. [imp. & p. p. Toned; p. pr. & vb. n. Toning.]

1. To utter with an affected tone.

2. To give tone, or a particular tone, to; to tune. See Tune, v. t.

3. (Photog.) To bring, as a print, to a certain required shade of color, as by chemical treatment. To tone down.

   1. To cause to give lower tone or sound; to give a lower tone to.

   2. (Paint.) To modify, as color, by making it less brilliant or less crude; to modify, as a composition of color, by making it more harmonius.

      Its thousand hues toned down harmoniusly.
      --C. Kingsley.

   3. Fig.: To moderate or relax; to diminish or weaken the striking characteristics of; to soften.

      The best method for the purpose in hand was to employ some one of a character and position suited to get possession of their confidence, and then use it to tone down their religious strictures.
      --Palfrey.

      To tone up, to cause to give a higher tone or sound; to give a higher tone to; to make more intense; to heighten; to strengthen.