Can Adirondack Alcohol Inks be used on metal?

Alcohol Ink can be used on metal, but if there is some type of coating on the metal it may rub off. Applying these inks to something that is handled frequently (such as a clasp) can cause the inks to rub off. Some surfaces have more tooth to them and the inks are able to adhere a bit better. You should avoid using these inks on frequently handled surfaces. If they will be handled a lot, we recommend sealing them (see below). It's also important to  remember that these inks are for decorative use and are affected by other solvents.

Does Adirondack Alcohol Ink need a special sealer to get it to stay on non-porous surfaces?

Although Alcohol Inks are designed for non-porous surfaces, if a surface is going to be handled frequently or subjected to other solvents from skin or other chemicals, it is necessary to seal it. The important thing to remember: DO NOT USE A SOLVENT-BASED SEALER (like Krylon®). Instead, use a water-based and waterproof sealer (like Mod Podge® or any other brush-on sealer from the craft store). Using brush-on sealers on something functional like a clasp is tricky as it can cause the mechanism to stick. If you want to "antique" your hardware, apply inks and sealer while the clasp is open and allow it to dry completely.