Glass in Corona: transparency and tint
For clear glass in Corona Legacy, enable Reflection and Refraction, keep Glossiness high and check the model’s thickness. For a tint that becomes stronger in thicker areas, adjust Absorption color and Distance. Simply coloring Refraction produces a different result.
Identify the material type and check the geometry
The following settings apply to CoronaLegacyMtl, the older material still found in existing scenes and asset libraries. Chaos recommends Corona Physical Material for new materials. Physical has a different interface; check before transferring Legacy control names and values.
For a vase, bottle or glass tabletop, check the actual thickness and whether the mesh encloses a volume. A single surface does not describe a solid glass volume. If the model contains cavities, check their boundary normals; do not flip every normal just to obtain one effect.
Thin window glass can use a simplified mode. In Legacy it is called Thin (no refraction); in Physical it is Thin shell (no inside). This mode does not reproduce true refraction inside a volume and does not replace solid glass in a close-up.
Build a basic clear glass material
Create CoronaLegacyMtl in the Slate Material Editor and assign it to the intended object. Keep Diffuse dark and the Reflection and Refraction colors white. Set Reflection Level = 1 and Refraction Level = 1.
For a smooth, clear surface, set Glossiness = 1 in both Reflection and Refraction. IOR = 1.52 is a useful starting point for ordinary glass; also check the reflection’s Fresnel IOR. This is a starting point for ordinary glass, not a recipe for every kind of crystal.
Start interactive rendering and inspect the shape, highlights and objects visible through the glass. Check the colorless base before adding frosting or tint. This makes it easier to identify which change caused a problem.
If glass turns black, check the ray path
In a complex shape, light crosses several glass and air boundaries. A Max ray depth value that is too low cuts off these calculations: some areas can darken or lose the content seen through them. The setting is in Render Setup on the Performance tab.
Compare values from the same camera with an unchanged material. Before reducing depth for speed, check edges, nested details and objects behind the glass. There is no universal minimum for a window, stacked drinking glasses and a decorative object.
If the entire scene darkens, also inspect geometry near the camera. An open surface using refraction or absorption may be interpreted as a volume surrounding it. For solid glass, fix the thickness and enclosed geometry; for a suitable thin surface, choose the thin-shell mode.
Frost the glass with Refraction Glossiness
Copy the working clear material and reduce Glossiness specifically in the Refraction section. The demonstration uses 0.6 as an example for frosted glass. Adjust it to the reference and object scale, keeping the original copy for comparison.
Place an object behind the glass and change the distance between them. Through a frosted surface, a nearby object may remain visible as a silhouette while a more distant one becomes more blurred. Do not judge the material solely by its small preview sphere.
In Legacy, lowering Glossiness increases blur. Physical’s default Roughness workflow runs in the opposite direction: higher roughness means stronger blur. Identical numbers in these fields do not mean identical frosting.
Choose Refraction tint or absorption through the volume
For a simple overall tint, change Color in the Refraction section. It colors transmitted light but does not by itself describe stronger coloration along a longer path inside the glass. Do not try to obtain that effect by brightening Diffuse.
For a thickness-dependent tint, return Refraction to white and open Volumetrics and SSS. In Volumetric scattering mode, adjust Absorption color and Distance. Start with absorption alone; Scattering color is unnecessary for ordinary clean, clear glass.
With the same color, a shorter nonzero Distance strengthens absorption and a longer one weakens it. Distance = 0 is a special value that disables the effect. Check the scene units: a suitable distance for a large test object may not suit a small vase.
Compare thin and thick areas of the model. With volumetric absorption, coloration should depend on the light’s path through the glass. If the entire object becomes too dark, check Distance, Absorption color and scale before changing the lighting.
Check the material in the working interior
Return the object to the final camera view and check its edges, highlights and background. Keep lighting, exposure and camera position unchanged for comparisons. A test shape helps explain the controls but does not replace reviewing the material in the actual scene.
Do not treat disabling cast shadows on all glass as a required step, or copy someone else’s ray-depth value into every project. These changes affect lighting and how objects appear; choose them for the specific image.
If you continue in Physical Material, create a separate material and compare the result. Check Refraction and Roughness for its clear base, and choose the thin-shell mode according to the geometry. Keep the working Legacy version until the new glass has been checked in a render.
Technical documentation: Chaos: Corona Legacy Material controls · Chaos: thin-shell and solid glass · Chaos: dark scenes and refraction issues
Related tutorials
Source of the article and frames: Romas Noreika — 3ds Max Corona Renderer Realistic Glass Material Step-by-Step Tutorial