A Grindstone is very simple to make and does not require much Starlight. It will allow you to enhance your tools (Pickaxe and Axe) and weapons. Throwing a sword in and then right-clicking the grindstone will make sparks appear. Once these stop appearing you can take out your weapon (sneak-right-click) and you will notice your weapon is now sharpened, which grants a 10% damage increase.
This works even better with Rock Crystal tools. Once you have created your Rock Crystal sword you can throw it into Liquid Starlight to increase its size further. Be aware that when you submerge Rock Crystals or Rock Crystal tools in Liquid Starlight it may increase its size but it will decrease its CUTTING unless the Crystal was split before hand. Size will only decrease when used in the grindstone. When the size goes down to 0 it will destroy the item.
The Purity of the Crystals can be boosted by “Splitting.” This process requires Rock Crystals to be thrown into Liquid Starlight. When the Crystals reach max Size they have a chance to “Split” (basically double). This process can be repeated but it will reduce the Size of the Crystal by a lot and will randomise the Cutting.
These weapons can be stronger and faster than their diamond counterparts but they will dull overtime, losing attack damage.