No need for additives. Hash rosin carts
How to make rosin carts with minimal equipment and a fully solventless process. The only input material is hash rosin and the ouput is full spec vape carts.
hashtek.ca
Or you can just heat rosin in the oven or on the press plates for flower and syringe it into the carts when it's thin. But you're gonna want to use the 37 micron bags or it'll gunk up
The whole process is a lot of work if you're just trying to use up some carts