Can be stacked with other defense boosting items including more Steel Nut Salve up to four times (multiplicative).
First Quarry Location
There is a 8% chance of it spawning in this chest. This location is to the left if you are entering from the north entrance.
Second Quarry Location
Go south from the first location until an impassible wall is approached. To unlock the wall, Promissory Notes must be purchased - after a couple of days the tunnel should be opened. There is a 25% chance it will spawn in the chest on the right.