Semi-Transparent Materials not rendering right

[bots (HettyGreen)]

I have a closed poly-surface that has a Material property of Plastic - with a semi-transparency. (The actual object will be made out of smoke-grey plexiglass). On the “Render” view, it appears perfectly. However, when I go to Render out a nice image using Rhino Render, any transparency is lost and the object becomes totally opaque.

[nathanletwory (Nathan 'jesterKing' Letwory)]

The Rendered mode and Rhino Render handle transparency different. I wrote about it back in 2017 - then for the Raytraced mode, but the same is pretty much true for Rhino Render.

Any plans to fix RAYTRACED mode or is it now where its gonna stay?

Raytraced handles transparency a bit different (for i.e. glass and transparent plastic materials). The transparency color should be regarded as a filter, where white lets all light through. This means that black lets no light through, no matter how high you set the transparency. Since the Rhino color shows RGB values in the range of 0-255 per channel we’ll use that for the rest too - internally colors are mapped to 0.0-1.0 where Raytraced actually can handle values outside the range (for high …

In short:

Create a material with 100% transparency, then assign a grayscale color to the transparent color channel. The (diffuse) color channel should be set to black - easiest is to just use a Glass (possibly Plastic) material, then convert that back to a Rhino Custom material and play with the transparent color channel.