Yeah, I overlooked that right-click menu too! Nice tip, thanks. Another way I noticed you can do this that I discovered after I posed the question is this: Open the Secondary Selection Pane and you can drag and drop a material into the ‘In Model’ group. You can do it in both directions, Primary → Secondary and vice versa.
I probably should explain why I asked about this, and admittedly it’s probably a weird corner case. It has to do with creating a material attribute list for a dynamic component. It seems you can’t create a list without materials existing in the model. So…the two tutorials/explanations that I read recently had you create little rectangles, add the materials you wanted in the scene, add the materials to the attribute list, then you can delete the rectangles afterwards. So, I suppose the authors of those tutorials sort of missed the boat in that they could have / should have told the reader to use the two methods here we have discussed- 1) RC menu ‘Add to model’ & 2) drag and drag between the two material editor panes. But you are absolutely correct; the purging of these materials could pose a problem afterwards. You can create the material attribute list for a dynamic component, but if the materials are not in actual use, they can be purged. Then you get some weird results. When you make a material assignment with your via Component Options the Default Material gets assigned if the material is missing, which I suppose is a reasonable way to handle it. Of course you could also say that you would probably not run into this issue because after a material attribute list is created, it would more than likely be used to assign materials before someone purged the file, but you never know.