Name Your Finish: With Gloss or Without
While 3D printers can reproduce objects of varying shapes, designs and colors, a glossy finish is still a challenge to be hurdled. 3D printing hardware cannot provide that shiny appearance as it isn’t designed to deal with the different viscosities of the varnishes that give surfaces a glossy or matte look.
MIT researchers provide the solution to this situation. They have developed a combined hardware and software printing system that uses ordinary varnishes to finish objects with realistic gloss patterns.
In what applications could this solution be useful? It might be used to faithfully reproduce fine art, and also help create more realistic-looking prosthetics. This is a step toward visually perfect 3D printing.
What gives a surface glossiness? Glossiness is a measure of how much light is reflected from a surface. For example, a mirror is very light reflective and has a high gloss surface. Varnishes that lend a glossy finish tend to be less viscous and to dry into a smooth surface. Concrete has a low gloss or matte surface which is unreflective. Varnishes that lend a matte look are more viscous, with large polymers that protrude randomly from the surface when dried and they absorb light. You may have a rough surface.
The problem is that the channels and nozzles of 3D printers are not designed for viscous fluids that can clog easily as they are small and narrow. To reproduce a surface with spatially varying gloss is labor-intensive. A realistic-looking 3D printed object will have high gloss areas and matt finish in others. A 3D printer cannot be instructed to produce a matte finish in one area, or a glossy finish in another. So the MIT team invented one.
They designed a printer with large nozzles that can deposit varnish droplets of varying sizes through a needle valve. A variety of droplet sizes is achieved by controlling the reservoir pressure and the speed of the needle valve’s movements. The more varnish released, the larger the droplet deposited; ditto with the speed of the droplet’s release. Halftoning is used to achieve spatially varying gloss. Discrete varnish droplets are arranged in patterns that appear like a continuous surface. The printer uses just three varnishes – glossy, matte, and one in between. The liquids have their preprogrammed halftoning pattern so the printer can yield continuous, spatially varying shades of glossiness across the printing surface.
The MIT team produced a software pipeline to control the printer’s output that depends on the user’s desired gloss pattern. The printer runs a calibration and based on the reflectance, it determines the proper halftoning pattern to use on the final print job. The team plans to continue developing the hardware for use on fully-3D objects.
