3D printing involves making an object layer by layer. There are many 3D printing techniques, and they all differ in how each layer is constructed. Each type of printer has a different opportunity or mechanism for adding color.
The simplest kind of 3D printing, that most people are familiar with, is extrusion-based printing or fused deposition modeling. These printers take plastic, melt it, squeeze it through a die and then lay out each layer.
In this case, the way to truly add color is by using colored plastic. If someone wanted to print more than one color, they would need multiple print heads, one for each color of plastic. Using colored material is the simplest way to get color in 3D printing.
The same tactic of using colored material works for stereolithography printers. These printers use a vat of liquid resin. Shining a UV light on the resin cures it, or hardens it. These products are also built up layer by layer, but instead of extruding plastic, resin is cured one layer at a time and the part essentially rises up from the liquid.
If you use a colored resin, you’d have a colored part. In that case it’s really hard to incorporate more than one color because the vat just contains one liquid material. You’d have to have multiple vats of resin or partially print something with one resin and finish it with another. People are experimenting with all kinds of ways to do that.
There are printers that do true 3D color. But all of them actually apply color the same way we have been applying color for years, using HP or inkjet print heads. One of the most common techniques is inkjet powder-based printing. This uses a print head that puts colored glue on top of powder. The final product is a beautiful, 3D color part, but it’s kind of powdery still. It has to be sealed with something like a glue.
You always need to find a way to construct a layer before you can add color, because color has to be incorporated into the actual 3D printing process.
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