Water Level

[Keith]

I have a '70s vintage century that flows decently, but the water level is about 3/4 of an inch below the cap. Is this normal, and if not should I use distilled water to top it off? or salt water with surfactant?

btw I have not opened a lava globe in 30 years!
ruined 2 when I was a teenager ;-(

[Ford Prefect - NPNG]

Hi Killer!
Its quite common for a lamp of that age to have lost a bit of fluid through evaporation over the years. if the level expands to meet the bottom of the cap when running, i shouldnt worry about it.
However, if it doesnt (and it annoys you) you can top it off. if you just use distilled water, it may 'slow' the flow, if you just use salt water & surfectant, it may 'quicken' the flow.
Personally, i'd top it off with distilled, run it for a few hours for a couple of days and see how the flow is. if it is too slow, i'd add a little bit (and i mean a little) of disolved salt solution (not table salt, i've used 'liver' salts before). you need to disolve the salts in distilled water before adding or it will wreck the wax.
if you add too much salts you will then have the annoying situation of balancing the fluid, which would take some time.
you shouldnt need to add surfectant at all, that affects the surface tension of the wax, but see how it goes.
remember to leave enough room at the top, so it should really be a little bit under the cap when cold.
hope that helps, i am no expert but i have done this recently and its been fine.
good luck!
Lucy

[Keith]

Thanks! I will try the distilled water in a few days and let you know how it went.