These lamps are supposed to be fillable. I don't know how because there is no base/ bottom on them, the bottom is rough & would scratch any surface. They are hand blown, (so no two are the same) - very thin & fragile.  Would NOT RECOMMEND . One arrived broken & Wayfair immediately sent a replacement BUT I didn't want them at all. We got things work out & I did receive a credit.
Thanks Wayfair - you are the best!