Enter Material Editor of the Group 1 and from the Shader drop down list select the Glass for objects material.
It is very important that you click No when Workshop ask you if you want to populate the material with the default properties. When you are finished, click on Done in the Material Editor.
You want Glass for objects material to be in this group only so select Yes when workshop ask if you want the material to be duplicated and linked to this group only.
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