I created a material that i like, and saved it to my library. However, the preview icon for it is a black square. How does one create a preview image for it? Is there a script i can get that will do this for me?

It should be created automatically when the material was saved to the library. I've not had this problem so can't offer a solution but if the material is loading ok when the icon is clicked you could create your own icon by doing a manual render and overwriting the existing png with the resulting image.

A single material will save as a single square, as an approximation - similar to Preview Mode - of how the material will look. Poser often can't show complex materials correctly in Preview, so you get these odd results sometimes. If you save a Material Collection, you'll get a thumbnail of the figure it was saved from.

Ironsoul's advice is the best way to go; it's how you'd do it for packaging an item to upload, free or for sale.

Thanks for the replies. I think i will have to do it manually. The material is a superfly material, and if I save it as a collection, I can't use it on anything but what i created it on, and it is black and white.

Whenever I hear Superfly, I just think of some African dude in a long coat, stack heels and a fedora.

Showing my age, I know.

That was my first reaction when i first heard the term. Actually, I still do also.