% Tone:           Minutes:Seconds
                                         Total           Add
                  10%  . . . . .     0: 13
                                                            0: 12
                  20%  . . . . .     0: 25
                                                            0: 22
                  30%  . . . . .     0: 47
                                                            0: 36
                  40%  . . . . .     1: 23
                                                             0: 56
                  50%  . . . . .     2: 19
                                                             1: 22
                  60%  . . . . .     3: 41
                                                             1: 54
                  70%  . . . . .     5: 35
                                                              2: 31
                  80%  . . . . .     8:  6
                                                              3:  9
                  90%  . . . . .    11: 15
                                                              3: 45
                 100%  . . . . .    15

                  Left column(%) is per cent of tone on a
   grayscale. Center column (total min:seconds)is
   total etch time for a % of tone. Right
   column (add min:sec) is amount of time to add
   to total time immediately above it to arrive at
   total time immediately below it. Maximum etch
   time is estimate, based on coarseness/fineness
   of aquatint, strength of acid, temperature,
   and any other factors which determine the
   maximum amount of time an aquatint can be in
   the acid before it reaches black and starts to
   break down.