I expose a UV device for gel nails (4x9 Watt; camp = 1638 & creative = 19454 & creativeASIN = B00MUBTMSS & Linkcode = as2 & tag = neighb-21 & LinkId = IK5W5WH5JCSPU7NP) 5 minutes (Bungard material) for perfectly sharp and disruptive results. Even large copper areas remain after etching with sodium (in a simple heated bowl) with no holes or corrosion condition.