A historical and technical introduction to gold surface enrichment. This academic paper describes the approaches that goldsmiths have used historically in various cultures to remove base metals from gold alloys for refining or "coloring the gold": depletion gilding. There is an extensive listing of recipes from numerous historical and contemporary sources to foster contrast and comparison and deepen readers understanding of the subject. It is intended for information only and is not a "how to" for depletion gilding. Many of the procedures described are hazardous and not to be done without a chemical fume hood and similar stringent precautions. 40 pages.