Popular recommendations can lead you astray. One example is the use of toothpaste to polish pens, and especially nibs and metal trim. Experts on antique silver warn against using toothpaste, but the websites I've seen don't explain why. So here's the scoop.
The abrasives used for toothpaste aren't carefully graded for particle size, unlike abrasives specifically intended for polishing precious metals and plastics. In large part that's because they are specifically chosen to be hard enough to scour off gunk sticking to your teeth, without being so hard as to scour off the hard outer layer of your teeth themselves. On a gold nib or gold plated trim, though, it's a different story. The toothpaste abrasive is much harder than those surfaces, and because the grit size is uneven, will remove an excessive amount of material while still leaving the surface covered with fine scratches.
Overall, you are best off using a jeweler's cloth -- the Sunshine brand being one of the most popular and widely distributed.
