Just stumbled on this for external glass - has been working well for me recently;
VRay Material
Diffuse
13 13 13
Reflect
106 106 106
Refract
253 253 253
Affect Shadows ticked
N
VRay Material
Diffuse
13 13 13
Reflect
106 106 106
Refract
253 253 253
Affect Shadows ticked
N
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