It appears that when I craft an elemental trap using a varnish, it consumes not one but the entire stack of varnishes. About 2 minutes after I realized this, I used the @debug command (doubt it'll be useful).
Where: Barovia - Village of Barovia - Mircea's Foundry
When: Any time I attempt to craft an elemental trap
What: I created three different trap kits from steel ingots - a one using steel spikes, another using fire varnishes, and a third using acid varnishes. I used the trap kit on the spikes, which worked just fine. I then used another trap kit on a stack of 20 Strong Fire Varnishes, and the third on a stack of 16 (I think) Strong Acid Varnishes. These created average piercing, average fire, and average acid traps as intended -- but in doing so, it appears to have consumed the entire stacks of fire and acidic varnishes. I crafted a fourth trap kit to test it out on a single varnish (split stack into 1 unit), and it appears to work as intended.