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The Dielectric material is a physically accurate representation of a non-conductive material. Basically this means it is great for glass and fluids.

Color: This is the colour that the refractions will be tinted to as the thickness of the dielectric increases.

Absorption: This value controls how quickly the refractions are coloured based on thickness. The higher the value the less thickness is needed to colour them. The absorption is handled by Beer's Law.

Refraction Index: The Dielectric material uses the Fresnel equations applied to the refractive index, to calculate the intensity of both reflections and refractions automatically.

Refraction Dispersion: Controls the amount that light is split up into its components as it passes through the dielectric. This will add a realistic fringing of red and blue to the refractions, also known as chromatic aberration.

Dielectric Preset Is a basic node graph to set up a simple Dielectric surface. You will have to make adjustments but this preset handles the air surface automatically.

Dielectric usage checklist
Raytrace reflection and refraction on in Render Globals Double sided on in Surface Editor (but no other changes needed apart from Smoothing) "Modern" Camera (such as Perspective)

This shows a Dielectric material with an absorption of 1.0. The thickness of the stalks varies from 120mm at the thinnest to 400mm across the end bulb. You can clearly see the thicker colour in the bulbs. This is handled by the node automatically.	This is the same Dielectric but with an absorption of 30. You can see clearly how the transparency has been much reduced but is visibly different through the thinner parts of the model.

This shows a Dielectric material with dispersion. The dispersion gives rise to the red and blue fringes visible in the image, and is a property of real world materials.