Incomplete lava flow??

[www.6-ft-under.com]

I have an old lamp....it came from a yardsale a few years ago. (Now you know as much about it as I do.) The problem is that it takes about 6 hours to start to flow (with a towel laid over the top to keep the heat in.) And even after it starts to flow about half of the lava stays at the top of the lamp. Even when the lamp cools it still stays at the top. Does anyone know what's up? Can this be fixed?

[www.6-ft-under.com]

HI Bohdan! Is it typical for about 1/2 the wax to lay at the top of the lamp? I am using a 40w appliance bulb also, as the 25w or 35w is impossible to find. They are neat lamps.....but very, very slow!