difference between opaque, semi-opaque and transluscent inks for sim and 4CP?

[blue moon]

There is a wide selection of inks. Some very accomplished printers are advocating the opaque type inks (MX for example) for simulated process.
Union has Unimatch system which they market as specifically for simulated process. These are semi opaque.
four color process is printed with translucent ink?

what's behind all that?

I know that semi opaque inks I use require a whiter underbase for the colors to pop. This requires a heavier layer of white and makes the print thicker than it could be. But there must be an advantage to it? What is it? And if there is an advantage to going semi, why not go translucent like 4CP?

ANy ideas?

Can any ink manufacturers or separations software writers explain why one or the other?

pierre

[yorkie]

The difference is a magical property of matter called transparency. When carbon sits in a random alignment, you see black coal, but if you crystallize the carbon, you get a transparent diamond. the difference is the atoms alignment to the matrix of reality.

With opaque inks, such as carbon black and titanium dioxide, a photon hits the atom and depending in the pigment, either be absorbed (black) or reflected (white). White light is actually composed a many different colors of light. For a colored pigments such as red, any none red light is absorbed, while all of the red light is reflected.

For transparent inks, the light is either absorbed or transmitted. Clear allows all light to pass, where translucent red allows red light to pass.

Translucent inks need something else to reflect the light. This can either be a white or light color shirt or an underbase. Process color was invented to allow a full spectrum of color to be created, which can be separated into film with a compute. In the old days, separations was done use colored filters.

Pigment inks directly reflect the light. Given an ample volume of pigment, pigment ink can be printed on black.

Now we get to semi-opaque. These inks are a compromise between transparency and opacity. Where a process color requires 4 screens to to produce a single hue, an ink mixing system can mix a single specific color semi opaque ink of a specific hue. The pigment density of these inks is not high enough to be truly opaque, so many times they need an underbase of white. By halftone the white, the darkness of lightness of the hue can be varied. This translates into a "race shirt" where the inks is produced with the team colors, then have the shadow detail of the car expressed in the white underbase.

The semi-opaque ink is also not limited to printing on white. When one color is printed on another color, a third color is created, but the top color will take priority, but exactly how much will depend on the specific opacity of the ink. This is where color separation software comes in. If a computer knows the opacity of the inks and is told how may inks can be used, the software can decide the best mix of colors and what order they should print. Reducing from full color to simulated process is not an exact science, so skill and experience can vary the quality of the results.

[tonypep]

At two different high end sim process shops overtime we struck off a grid from 5% halftones to 100% coverage in 5% increments using literally hundreds of color formulations within a given ink system on 100% cotton black jersey fabric and then with a white underbase using the same grid then printing those same colors with a one hundred percent overprint also on black fabric (yes this took a while).
Why? Well the truly good separators often found in the music and entertainment merch companies do not use separation software. They build the seps "manually" in Photoshop and Illustrator. At OATS and Winterland we used to say "you're only as good as you're underbase". Or the percentage tone underbase to be exact. See the percentage of halftone underbase under overprint color yields different shades and tints of said overprint color; resulting in a wide range of color pallette utilizing a fixed number of allowable screens.
So the above excersize would help the separators understand the transparent/opaque properties within a given ink system which in turn helped them to better predict the outcome of their work.
That said an ink that is too transparent is less desirable for sim process on darks. Conversely the super opaque inks can be problematic as the higher solids can result in unacceptable dot gain and ink build up on succesive screens. So the semi-opaque series; in my opinion, are ideal for sim process on darks.
And of course for process on whites the inks must be transparent (or translucent to be more accurate)