From LSWiki

Aperture: Alloy

Alloy focuses on the capacity of one's lens to be shaped into enduring objects, and more generally the capacity of light to interact with metal. This aperture enhancing one's constructs and ultimately gives one a greater leeway to interact with ferrous materials.

Primary Skill  : metal affinity

• Tier 1  : lesser smithing specialty access, access to the Repair volition
• Tier 2  : major smithing specialty access, access to the Empower and Balance volitions
• Tier 3  : greater smithing specialty access, increased tolerance to ferrous materials

Notes

• Without any metal affinity and lacking tier 3, even the slightest amount of ferrous metal worn or wielded on your person will strongly disrupt your lens.
  • With 40 metal affinity and tier 3, most ferrous weapons can be wielded.
  • At or around 200 metal affinity, you may wear an adamantine full suit while wielding Strangmacht completely drunk on quicksilver.

• Sadly, it seems like despite the description this apterture does not grant your constructs or powers any further ability to interact with ferrous material based on metal affinity. At the very least, at 250 affinity I was still seeing weapons and powers turned away from iron gear.

• Tier 1 grants 3 access, tier 2 grants 6, and Tier 3 grants 10 access plus 1 bonus specialty in both Metal Affinity and Smithing.

-Shinichi