Awards & Engraving

October '18

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A&E OCTOBER 2018 • 21 Laser Engraving a drawing engraved on a dark-colored, powder-coated tumbler results in a flag with dark stars on a light field, seven white stripes, and six darker stripes. And a bald eagle will have a dark head and a white eye on a dark-colored, cotton duck canvas bag. While the white text on glass is, in prac- tice, acceptable, the others are not. I've seen enough negative flags and black-headed bald eagles to know that this is an issue. ACCOMPLISHING INVERTED GRAPHICS Inverting graphics is simply another term for changing a drawing or a graphic compo- nent from a positive image to a negative one. It's accomplished in graphics programs by selecting an object and using a tool or func- tion that converts that object to a negative version of the original. In some programs, it's known as inverting colors; in others it's simply called negative. Regardless, the graphic's color values are reversed. It's usu- ally best, for the purpose of engraving with the laser, to have the graphics in black and white or grayscale before inverting. Many clipart graphics are in black and white and can be inverted without much of a problem. Some, however, are just black, with the white parts of the drawing being empty spaces. Invert them and the graphics "disappear." The black areas are now white, and the empty spaces are still empty. The same happens with black text. To get a nega- tive image, you need to fill the empty spaces. This is done for most graphics by adding a white background to the original graphic. A white border can also be added, particu- larly around text, to differentiate it from the background of the piece being engraved. The tiles in the photo above demon- strate the need for inversion and some of the problems you can have inverting graphics. The white tile with the black image is actu- ally a black tile painted white. The engraved image is made by vaporizing the white paint and exposing the black tile underneath. The graphic in the drawing looks just like the engraved image. Engraving this tile is akin to drawing on a white sheet of paper with a black pen. That same drawing will get similar results on other materials where the mark will be darker than the material being engraved. It's a straightforward pro- cess with no inversion needed. The black tiles are white ceramic tiles painted black. For those, the laser removes the black paint exposing the white tile underneath. The laser is making a mark that is lighter than the material. It's equivalent to engraving on materials such as dark-colored tumblers, dark-colored cotton duck canvas, black granite and glass, or clear cast acrylic. The tile in the upper right of the photo was engraved using the same graphic that marked the white tile. The engraving, while recognizable as a ram, is clearly a negative image. In order to get a positive image of the ram, the graphic in the drawing must be inverted. But, as you shall see, it's not that simple. The lower left tile in the photo was engraved with the graphic in the drawing inverted. The engraved image is a positive; however, two of the legs and the tail have been lost from the engraving. They are still there in the drawing, but because they are the same color as the background, they cannot be seen. Fixing the lost parts is fairly simple. The lower right tile was engraved using an inverted image with an outline, which defines the limits of the shape of the legs, tail, and everything else. The outline in the drawing is black, thus it draws on the tile exposing a white outline. An alterna- tive would be to create a background shape filled with black or even a gradient. So be aware that outlines or back- grounds may have to be added in order to set the engraved image apart from the material being engraved. "If the mark is lighter, invert away. If it's darker, let the graphics stay." DEALING WITH DIFFERENT MATERIALS How different materials react to being engraved by a laser determines whether a drawing should be inverted or not. Some materials engrave darker, some lighter, and some can be a toss-up. Here are a few common material types and how to deal with them. For color-coated tumblers, every time black text in a drawing is rastered onto a dark color-coated tumbler, a negative image in stainless steel or aluminum is created. With text, that usually isn't a problem; it's the contrast that is important. If, however, The tiles in this photo demonstrate the need for inversion and some of the problems you can have inverting graphics. See text for details as well as how to correctly do so.

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