The Linking Tool is an item added by Astral Sorcery. It is used to direct Starlight from a Collector Crystal, Celestial Collector Crystal, Lens, or PrismLens to a block. Right-clicking on one of the aforementioned blocks with the Linking Tool will display a "Selected <block>!" message in the chat log. Right-clicking blocks will direct a ray of starlight to the selected blocks with the text "Linked <block> to a block!" Shift right-clicking on the starlight-producing blocks will erase all existing starlight rays and display the message "Unlinked all links!" in the chat log. Switching to another item will display "Stopped linking!" in the chat log and finishing the linking process.
Due to the attractive effect that Aquamarines have on Liquid Starlight, using multiple Aquamarines should allow you to control and tune the Starlight energies emanating from a Starlight collector. Fusing them with a Rock Crystal to build the proper resonant structure will be tedious without sufficient Starlight. Luckily, the recently upgraded altar should help on that end.
However, holding the fused crystal with bare hands runs the risk of clouding the crystal, and therefore diminishing the ability to manipulate Starlight. As such, the most practical form of a Linking Tool takes the shape of a wand. The crystal wand created by this fusion of gems seems to bend Starlight around it at will, persistently altering the flow of said light. Linking a crystal to multiple destinations will split the flow evenly across all of them, even if all links are not in use or are obstructed.
To select the source of Starlight, simply right-click the Starlight producer, such as a Collector Crystal commonly found in a shrine. To direct it to a specific location, right-click the other location(s) afterward. To dissolve the link, right-click the destination location while holding Shift. To deselect the source and stop the linking process, change the active item to another item.