Once you have collected all 5 items belonging to a collection, you can combine the collection in the collections tab to receive your rewards. In order to combine any collection you will need a set amount of 4 different combining elements. Combining elements are rewarded to players for successful investigations of pictures and puzzles. Combining elements may also be found inside some chests. Combining elements can be gifted to your friends as free gifts that do not come out of your inventory.