Explanation of the mapping:
If an input atom is salt it does nothing.
Start with lead-lead.
Input from left to right does:
Atom 1 fire project left by 1.
Atom 2 fire project right by 1.
Atom 3 fire project left by 2.
Atom 4 fire project right by 2.
Atom 5 fire and atom 4 salt project right by 4.
Atom 5 fire and atom 4 fire and atom 3 salt project left by 4.
Atom 5 fire and atom 4 fire and atom 3 fire project both by 2.

The missed inputs are silver-lead, silver-tin, gold-lead and gold-tin.
This is because the left atom can only get up to silver and gold when atoms 4 and 5 are both fire while atom 4 already makes the right atom iron.

Instead of conditionally using the quicksilver it's more efficient to create silver and iron from atoms 3, 4 and 5 and conditionally throwing it away instead. Only atoms 1, 2 and the both by 2 case from atom 5 have conditional quicksilver.