Nice lamp!! That's a 52oz Century. I have one w/ blue liquid/white wax from the mid 90s. The 1st 2 pics didn't upload...can you re-post them?
If the top decorative cap does not lift off exposing what looks like a beer bottle cap underneath, then it is a screw off cap. I wouldn't add anything to it though if its flowing. It may make things worse. Make sure to run it for a good 8-10 hrs at a time for a few days and see if the flow improves. Mine acted the same after it sat idle for years but after cycling it a few times its now going great again.
It looks great to me !! enjoy !
most of my older lamps (90's) alternate between columnar and "blob" flow. i actually love the columnar flow, so it looks great to me. as for it being low, many older lamps are like that. personally, i would not add DI water.
if you want more spheres and less columns, you need a higher wattage bulb. if you were to add a dimmer or lower wattage bulb to the globe, it may not flow at all. it would likely just dome at the bottom.
Flows great! i wouldnt add any water just because "if it aint broke then dont fix it" also a higher wattage may end up cooking up the wax and ruining it if it overheats, i would run it for about 8 hours at a time, more than that and youre risking cutting the life of the lamp short by cooking the wax too much. The color is great.
Usually wax that gets cooked wont nessesarily look a specific way and i wouldnt say it happens after overheating once but most likely after several years of abuse. Usually cooked wax doesnt flow as good, sometimes it has almost like texture to it, it would look like it has flakes floating within the wax, i also beleive foamy or bubbly wax could be from extended overheating, but nobody knows for sure. I would keep the original 40w and if you want get a table dimmer to control the temperature to a certain extent.