My solution takes the input string and feeds it through a binary decoder, but with a funny position value order the fist atom that gets read is worth 4 quicksilver, the second 2, the third 1 and this determines the first metal, the  last two atoms are worth 1 and 2 quicksilver respectivly and makes the second metal. 
now if the first 3 atoms have combined value of 6 or 7, i subtract 2 and swap the order of the metals outputted. The subtraction is implemented by always trying to not project with the next 2 quicksilver if the first atom is fire. and then having a sucessful subtraction works as a check that the second atom was fire, this effectivly checks if the first 3 atoms have a value of 6 or higher. Then there is just some conditional bonding to swap the atom order.

This results in a valid encoding with the only missing metal combinations being: Silv-Silv, Silv-Gold, Gold-Silv, and Gold-Gold.

I had a few ideas about what encoding i would use, with my first one being to try and implement a base 6 doubble dabble algorithm, but after brainstorming a bit i settled on this: If >6 then sub2 and Swap approach instead.

This puzzle was made slightly more dificult for me by the fact that i didn't want to try to get into modding OM, so i just used the provided stabilized salt and some easily modifiable instructions to build the different input cases and test my solution that way.

This is the puzzle i had the most fun with out of every puzzle i have made. At first i only expected to make a solution and have that be the end of it, but i had the optimizing nag and then through a stream of small improvement somehow ended up shaving off 60 Sum over the course of a few days landing it squarely in the sub 600's, giving this solution that i actually feel proud of having made. I will not doubt the wizards having made much better this time, so i exditedly await to see just how low this sum game will go. 
Thank you for having me, and Thank you for a very fun puzzle.