helpful when your test print is far from being correct. When using a ring around, you should match the test print as closely as possible to one of the prints. The amount and color of filtration you should add or subtract from the filter pack are the same as indicated on the ring around. When the test print is reasonably close to being correct, you can predict the final exposure conditions accurately.  Once  again,  remember  how  exposure  affects the three dye layers of the paper. That will simplify the choice  of  selecting  the  correct  filtration. Color  Printing  Viewing  Filters When a test print is reasonably close to the desired color balance, viewing it through color printing viewing filters helps to determine what color change is needed. Color printing viewing filters come in six filter colors: red,  green,  blue,  cyan,  magenta,  and  yellow.  Each  color is represented in 10, 20, and 40 density values. To use a filter, hold it several feet away from the print and light source. Quickly flick the filter in and out of your line of vision to see the color correction the filter makes. Since these filters tend to overcorrect the highlights and undercorrect the shadows, you should view the lighter middle tones through the filters to determine the desired color balance. Try several filters of different values and colors when evaluating a test print; for example, when the print looks “cold” to you, evaluate it through a series of red, magenta, and yellow filters to determine whether the color in excess is cyan, green, or blue. Similarly, viewing a “warm” print through cyan, green, and blue filters will determine whether the color in excess is red, magenta, or yellow. Since the contrast of print materials is fairly high, a filter used in exposing a print tends to produce a greater change in color balance than the visual effect of viewing a print through a filter. In general, the filtration change to the filter pack should be one half of the viewing filter that makes the lighter middle tones of the test print appear correct; for example, you have determined that when viewing a test print through a 20CC green filter, the color balance looks correct; therefore, you would make a 10CC change to your filter pack Suppose, again, that the test print is too blue; that is, not enough yellow dye was produced. The print will look best through a 10CC yellow filter. Since blue light creates yellow dyes, we must increase the amount of blue light reaching the paper by 05CC. You should do this by subtracting 05CC of yellow filtration (for subtractive printing) or subtracting 05CC of blue filtration (for additive printing). When a 20M filter is best for viewing, subtract 10CC G (additive printer) or 10M  (subtractive  printer)  from  the  pack  to  produce  the desired  correction. MODIFYING  THE  FILTER  PACK Remember, you must produce a test print with proper  density  before  you  change  the  filtration  on  your enlarger or printer. Before modifying the filter pack in the enlarger or printer, you must keep in mind what type of printer you are using. Modifying the filter pack for a subtractive  type  printer  is  completely  opposite  from  the filter  pack  adjustment  necessary  on  an  additive  printer. Subtractive  Printers  or  Enlargers When you have determined what color dominates the test print, that filter or its complement must be added or subtracted from the filter pack Whenever possible, you  should  subtract  filtration. Table 12-1 may be useful in determining what filter adjustment  should  be  made. The following rough guide may also be helpful: When a slight shift in color balance is needed, use an 05 or 10 filter change; when a moderate shift is needed, use a 15 or 20 filter change; and when the shift required is too large to estimate, try a 30 filter change. The filter pack should not contain more than two colors of the subtractive filters (yellow, magenta, or cyan). When all three colors are in the filter pack neutral density results. Neutral density only increases the exposure time required. Neutral density is eliminated by removing the filter color of least density completely and then removing the same amount of density from each of the other two colors. Thus, if you calculated the filter pack to be 30M + 20Y + 10C, you should remove 10 CCs of each color (10C + 10M + 10Y) completely for a filter pack of 20M + 10Y + OC. When  you  either  add  or  subtract  filtration  from  the filter pack, the intensity of the light also changes. When filtration is added to the filter pack, the intensity of the light reaching the paper is less. When filtration is subtracted from the filter pack, more illumination reaches the paper. Thus you must adjust the exposure time when the filter pack is changed. Fortunately, when dichroic filters are used, little exposure compensation is needed. When these filters are used, no correction is required when the yellow filtration is changed. Only a l-percent change to the exposure time is required for each 01 unit of magenta or cyan 12-8