<p>I made a torus that was 1 on the x and y axes, and 3 on the z axis in Blender. It is supposed to be a bead for a beaded necklace. It was exported to Cura as an .stl, then printed on a Lulzbot Mini. It worked fine in plastic, but when we tried it with bronze filament the nozzle clogged and it didn't start printing.<br>
Is there something I need to add to the model that will provide instructions for the printer? The person who operates the printer says that most, but not all, of the models he prints in bronze have a border around them when they print, and this one didn't. I don't know if that makes a difference.</p>

We print a lot of stuff in a variety of materials, and I think it is likely what you are experiencing is a problem caused by some combination of the following: Object size overall, object detail size, wall thickness, or span width/thickness.
Blender gives pretty clean stls, but the last-mile needed to get output is primarily a materials engineering problem.... (and saying thias, I am assuming you got a valid stl that the printer was able to read and rip...)
A first thought: Try loading your stl into one of the services that price online. Shapeways does, and Cubify does or did... and you can download the driver software for the Form2 even if you don't own the printer.
Bring your stl into these apps and look for error messages. The Shapeways ordering app does a nice job of showing issues, particularly ones like wall thickness and manifold faces/vertices (another possibility I did not mention above) very quickly.
I'd offer to look at your stl if it is something you can share... and/or you can ask your output guy for a sample stl he has printed with some success before. Bring that stl file into Blender beside your model and compare.
I do not recognize a "border" around stls, but all of the printers have preferences for the support sprues that support the model as it is built.... possible that he means these?
In any case, shout if I can help. We have used a lot of materials, but some of them take tweaking -- most often with detail size (how small of a detail you can recreate on the rpinted surface) and step size (how small the steps are inbetween printed layers in additive rinting systems.
Or... just chuck it onto a CNC with a big ole' block of bronze and machine it down!  That's pretty old school, but it works, too... just by removing material rather than adding.
Here's a torus at Shapeways I uploaded....