Chemistry Sets are recipe items that have varying inputs and varying outputs. A Chemistry Set can be completed by fulfilling all of its inputs, which will then give the items it has listed in its outputs. There is an indicator in the upper left corner of the Set's inventory icon indicating the number of inputs possessed. Chemistry Sets can reward a Strangifier for the item the set is associated with, which, when used with the item, will turn it into a Strange variant; or a Collector's quality version of the same item.
Selecting the item and clicking inspect will bring up a GUI with all compatible items on the left, slots for the ingredients on the right, and the result under the ingredients. If it is a standard Chemistry Set the result will be the strangifier for the item specified in the set; unless it is a Collector's Chemistry Set, in this case the result will be a Collector's version of the weapon specified in the set. Items from the left side of the screen can be clicked and dragged over to any space on the right which requires said item. Once all spaces have been filled, the result will become highlighted and the "APPLY" button can be clicked, consuming all the items and the chemistry set. After the crafting is completed, the item will be put into the user's backpack and the user will be shown the new item screen and be given the option to resume game or open the player's backpack.
Players do not need to input every item at once, it is possible to select only some of the compatible items to be placed into the Chemistry Set. This will delete the items as normal as well as remove those inputs from the requirements of that Chemistry Set.