While working at Formlabs, I developed an interest in recreating an SLA (stereolithography) print material in Cinema 4D. SLA prints have interesting features such as small layer lines, subsurface scattering, and translucency that posed a challenge.
Here is my process in re-creating an SLA print material in Cinema 4D and Redshift.
The first notable characteristic of SLA prints is its translucency. This happens because light penetrates the surface of the print, is then scattered by interacting with the material, and exits the surface at a different point. This results in a lighter color in thin parts of the print and in darker color in its thicker and denser regions.
In order to achieve this effect in Redshift, I applied subsurface scattering (SSS) to the material. I started off with a completely blank material and only applied a Transmittance Color (the attenuation color) in the Sub-Surface section. I chose purple, but this could be any color you want your object to be. Your print will get its color from the SSS Transmittance Color when light penetrates its surface, and not from the Diffuse Color channel (so set that one to 0).
I set the Absorption scale to the approximate size of the 3D object in Cinema 4D so light would be able to pass through the entire object and set the Scatter scale to 1.7 to make it appear cloudy inside. Note that SSS behaves very differently based on your lighting setup. A light source placed directly behind your object will make thin edges appear significantly lighter than a front-facing light source, so work with the lights to get your desired effect. In this case, I placed three lights: one directly above the object and two more, one on either side. These are the results so far.
You can already start seeing the wax-like material with its lighter edges and light absorption properties. The default Reflection channel gives it a really glossy look right now, which we will take care of in later steps.
Optionally, we can set a Back-lighting/Translucency color to push the thin edges' translucency even further. The color you apply here will be the back-facing diffuse color of the surface, so set it to a lighter version of your desired object's color. This will emulate a cheap subsurface scatter that works well for thinner parts. This effect adds a lot of value in cases where there are paper-thin edges, but for denser objects like the one used in this demo, a true SSS should be used to simulate real light absorption. I've explored setting a light purple to 0.25 opacity to add a very subtle extra translucency to the material.
SLA printers create incredibly small layer lines on their prints since they print one layer at a time with a precise laser. They are less noticeable than on DLP or FDM prints, but they can still be seen on macro shots.
Those small layer lines also affect the way light reflects on the part. Those tiny bumps reflect light in a less uniform way than a smooth surface would, making it less glossy and more rough.
To add this effect to my material, I added a normal map simulating the surface of an SLA print. I used Alan Warburton's excellent normal map which also has imperfections representative of what we would get in the real world.
Those layers lines really muted the reflections on the print and added significant roughness, even when scaled down to microscopic levels. Since real SLA prints come out of a tank of resin, they are usually covered with a very thin layer of that shiny liquid adding a bit more gloss.
During post-processing, parts are also often sanded and coated with an oil to smooth out the surface, bringing back some glossiness and creating a more even finish.
In order to achieve that, I added 25% of Coating in the Redshift material.
While the SLA printers can create incredibly detailed and precise small parts, no physical object is perfect and no edge or corner has perfect angles. The final step in this material study is to add the same imperfections that you would see on an SLA print.
90-degree sharp angles have a very small bevel to them, which is subtle but still affects how light hits the object and corners. I have added a RS Round Corners node to my material to emulate a similar bevel. For objects such as the one used in this demo, there is very little difference since, other than its base, there are no sharp corners. You may find this useful with yours.
Product photography is often perfect and without scratches. However, there are often cases where it's nice to have them. Objects are also more susceptible to get scratches on their outer edges if they were to have any. I fed a B&W JPG texture of scratches through an RS Curvature node to apply them only to edges with a certain angle. I also applied that same texture to my main material's Reflection Roughness map to add a few more imperfections on top of the layer-lines bump map. The result gives a nice subtle yet realistic look to the material.
This experiment was a very fun and challenging one as it pushed me to examine this material's unique properties and use my understanding of Redshift to recreate them. While it certainly isn't a perfect representation of how an SLA print looks and behaves in light, I think it does a good job at mimicking its most notable characteristics for this demonstration.
Here is a screenshot of the final nodes to make this Redshift material. You can also find the source files and the created Redshift material to download here.
I applied that material to different objects and even did a 1:1 comparison with a real picture from Formlabs.com You can see below how that material compares itself to a real print.