While bonding to nonprecious alloys is relatively easy, concerns about the health effects of their base metals have caused a resurgence in the popularity of precious or noble alloys, notwithstanding their rising costs. However, bonding to precious alloys has been challenge.
Approaches to this task include conventional sandblasting, sandblasting with unique products such as CoJet or Rocatec, or tin plating. While none of these approaches are particularly difficult or expensive, using a simple primer as you would with silane on porcelain is certainly easier.
These products are designed to basically allow you to bond to precious alloys as easy as you do to nonprecious. We tested the bond strength of these products after sandblasting nonprecious, semiprecious, and precious metal. However, the longevity of the bonds is unknown.