There's been a significant number of posts in the separation section on how small a dot you can print and the value of carrying the partially 1%-3% dots. There is a solution to this and it may be a bit out of the ordinary, so a little background info is in order.
The halftone process is all about fooling the eye into seeing various tints, tones, and shades by mixing a solid printed area with unprinted area or by blending varying amounts of two or more colors to create the appearance of a new color. There are two ways to do this. The first is to simply change the size of the dot as it moves from 0% coverage to 100% coverage for any given color. This represents a specific percentage of the specific color. It does not represent the accurate tonal percentage of the color. This is accomplished by using Curves or Levels to change the size of the printed dot so the end result is what we want.
We can only do this to a limited degree. If we want to make a very light pastel color, we cannot reduce the dot enough before it becomes unprintable. So we change the ink color.
For instance. If you look at three different colors of red, Pantone 183, 185, and 187. A 50% dot area of each ink will give you a very different representation of the tone moving from pure white to pure black. It is entirely possible to have a 100% saturated red with 0% brightness. To our eye, it will appear to be black, but a very special kind of black. It is called a "Chromatic Black" because it is nothing more that 100% color with 0% reflection to our eye.
The second way to fool the eye is to manipulate the brightness of the reflected image to represent the tonal value we want to reproduce. So, for the example above, lets assume that Pantone 185 printed at 50% represents the target color value. If Pantone 183 is 50% of the optical value of 185, to get the same visual representation, we would print a solid of 183 to represent the targeted value (twice as much area covered.) Likewise, if 187 is twice as dark as 185, we would only need to print a 25% dot to achieve the desired target color.
So, we can create the same visual response to the eye by either printing:
183 @ 100%
185 @ 50%
187 @ 25%
Almost all printers concentrate on controlling the physical dot gain of the halftone without considering the impact on the overall tone reproduction. If the image is too dark, they will often put a lighter ink into the screen in an attempt to lighten the image. They will be able to lighten the image, but at the expense of contrast. By lightening the image, you flatten or lower the contrast in the shadows. You never achieve the dark colors, and you lose the relationship between the 3/4 tone (75% value) and the solids. The overall effect is a lighter, flatter, washed out looking image.
Here is how to overcome this problem, use a wet mixing white to control the dot gain in the highlights and quarter tones. This is how it works, but first some basic color theory.
When a color is perfectly pure, at maximum intensity, it is said to be 100% Saturated. If you add black to a pure color, you are shading it. If you add white to a color, you are tinting it. In either case you are desaturating the color. The same thing happens when you dilute color with halftone base.
The human eye has a hard time detecting 100% pure colors in very light values. We perceive these colors as tints or pastels of the pure saturated color. This is where we begin to derive our approach. When you look at the actual saturation values of these tints, they are often well below 50%, sometimes down into the teens percentages.
The colors you choose for your separation should be as saturated as possible for the image you are trying to reproduce. I don't want to get into separation theory, but lets continue with our example from above. The Pantone book has lots of problems, but this is one area where it works well.
Almost all the colors in the Pantone book (up to the 400's at least) are arranged on the page with the most saturated color as the middle of the page. Values going up have various percentages of white mixed in (tints) and the colors at the bottom are shades with black added to the saturated color. I want to concentrate on the top of the page.
You can experiment with this on your own, and I recommend that you do. Take any saturated Pantone Color and mix various amounts of white and various amounts of black and see how many different colors you can achieve using only color, white, and black. You will be amazed at the range for some colors. You'll get a hint of the outcome by looking at the pages in the book for the saturated color.
The idea here is to use a wet translucent mixing white to knock back the dot gain that occurs in the highlight area. The addition of white to ANY color will radically change the value of that color by turning it into a tint of that color. Now here is where the beauty of this comes in.
Lets say, from our example that Pantone 185 + a certain amount of white = Pantone 183. And Pantone 183 is a 50% saturation and 50% tint of Pantone 185. This means that if you print a 4% dot of 185 and mix it with wet white on the shirt, you will create a completely reproducible and predictable 2% pastel value. This was only an example, but the fact is, most primary colors printed with wet white will delivery fractions of a 1% optical value when the final image is viewed.
There is one MAJOR factor to consider. This is called the tinctorial value or tinctorial index of the pigment. Each and every pigment has a different value. Some are VERY low, like many of the blues. violets, and purples. Some are very high, like the yellow, oranges, and reds. To determine the tinctorial value (roughly) of a specific pigment, look at the tonal steps on the Pantone pages for a specific color. Some pages progress naturally toward a pastel and other pages have huge jumps with just the slightest amount of white added to the ink. Look at Pantone Violet and Pantone 072 pages for example.
Bottom line from this, you should always use a wet white in the separation sequence, even on white t shirts if you are concerned about creating a full and complete tone range from pure whites to solid blacks. This was a very brief and conceptual introduction to tone control. It goes much, much deeper, but this should give you an idea of what you can do to instantly improve your separations and extend the range of reproducible colors and tones in your images.
