Cast Welding Jar either from your hand or from the top of your library by paying 0
Showdown of the Skalds triggers, putting a +1/+1 counter on Arcbound Reclaimer.
Activate Welding Jar by sacrificing it.
Activate Arcbound Reclaimer by removing a +1/+1 counter from it, putting Welding Jar from your graveyard onto the top of your library.
Repeat.
This loop is a masterclass in recycling, turning the free-to-cast nature of Welding Jar into an engine of endless triggers. Madame Web, Clairvoyant provides the crucial top-deck visibility and permission to cast the Jar right off the top of your library, while Showdown of the Skalds rewards each of those casts by feeding a +1/+1 counter back onto Arcbound Reclaimer. Whenever you need to loop the artifact, Arcbound Reclaimer strips off that newly minted counter to place Welding Jar right back on top of your library, where Madame Web makes it immediately accessible once more.