Etching, A Synergy Question

I just crafted a fresh Sarissa for it's appearance. I wanted to etch it for fun but as soon as I traded it to the Synergy Engineer, he says "Alas it's a shame but it appears your Sarissa cannot be etched."

I know for a fact Sarissa can have 3 etchings for evoliths and I just got mine so it's not augmented. Any idea? When I trade my Sarissa and a Mordant 75 to the furnace, it says "This item cannot house anymore apertures". The thing is, when I check my Sarissa it doesn't have the blank dash lines indicated an empty slot?