Can you help ID please

[Miller]

About 40 years ago when I was a teenager I found under ground,in front of a old gold mine in California a old electric lamp. It had a glass cover and brass cage so the bulb was protected.  Using a rheostat to reduce voltage, the bulb works fine.  I am donating it along with other artifacts to my sons Fourth grade teacher who teaches and lives California history. The bulb has NO markings, except the number 520 on top of the glass tube inside. It has a cotton substance inside the glass tube. The wires appear to be solid ( material is ? ) It is about 4 1/2 inches tall, brass threads. Is it possible to tell the manufacture, and approximate age?  I'm assuming it is a common bulb.
Last, it is safe to use a rheostat so he can turn it on each year to show the kids?

                                                                       Thanks in advance, Herb Miller

[Tim]

I?ll take a stab at it.  This is most likely a product of GE, Westinghouse or similar conglomerate.  It?s hard for me to tell who made it without some kind of obvious identification label present on the bulb.  If it were an earlier bulb, then identifying it based solely on unique features becomes a little more easier to do, but not one from this era (for me anyway).  As for age, I would approximate early 1920s based on the design of the tungsten filament and overall appearance.  What is interesting to me about this bulb is the newer filament design combined with the retro exhaust tip.  I think this solidly dates the bulb to the early 1920s, but we?ll leave it open for debate here?

Below I posted on Oct 30th trying to ID a bulb. No reply, but does anyone have an approximate age of this bulb.
See post on 10/30 for pictures. Thanks for any help you can provide.

[Miller]

Does the exhaust tip mean it is hand blown?   Why the cotton inside the glass tube.      Thanks much

[Chris Kocsis]

The filament is of the single-coiled type, which was used in 100-watt bulbs in 1917 and in smaller wattages a little later; the bulb is likely gas-filled; and the envelope was most likely blown by machine (these machines were introduced about 1917 and gained popularity for the next few years).  So I would guess it was made in the late teens to early twenties (when the tips disappeared).

The cotton is simply to keep the long lead-in wires from touching each other.

Best regards,

Chris