Making a lens

[rich59]

It would be kind of satisfying to make my own lens.

One way would be to take a piece of ordinary glass and rub it down I guess. Anyone tried this?

More exciting would be to melt down some glass and reform it.

More dramatic would to be to take primitive materials and make my own glass. How could I generate the heat? Could I do it with DIY materials and simple fuel like wood or charcoal?

I tried heating a piece of glass in a flame from a candle for a while but it did not in any way change or go soft.

 

[led]

I'm guessing that making a lens from glass is going to be quite a job without some more specialist tools. Have you seen the tutorial on making a lens from ice? http://www.primitiveways.com/ice-fire.html

 

[Swampy Matt]

More exciting would be to melt down some glass and reform it.

More dramatic would to be to take primitive materials and make my own glass. How could I generate the heat? Could I do it with DIY materials and simple fuel like wood or charcoal?

I tried heating a piece of glass in a flame from a candle for a while but it did not in any way change or go soft.

It's possible to melt glass (a beer bottle) using charcoal, a barbeque and the foot pump for an inflatable bed. (DISCLAIMER - possible, not necessarily sensible!)

i'd assume that this could be adapted for 'primative' materials, or using common bushcrafting kit (a waterproof canoe sack can be used as a bellows, instead of the footpump).

I'm not sure if this could be used to make a lens though.

 

[daved]

Try a web search on telescope making and lens grinding and that should give you a few pointers. Here is a link to one of sites I found but you should be able to find others:

http://bobmay.astronomy.net/refractor/Refrindex.htm

 

[Grooveski]

Early lenses were commonly made from Rock Crystal(a form of quartz) ground to shape in much the same way as polished stone axes.

A shallow depression in a grinding stone(harder forms of sandstone work quite well) is used and the crystal ground down from a pebble to the desired shape. Once shaped fine sand and water is put in the depression and used to polish the lens to a final surface. As with knife sharpening, using a sequence of courser then finer sands is better than trying to go straight from a rough grind to a polished surface.

Finding rock crystal is tricky. I found a couple of decent pieces among thousands of quartz pebbles on a beach in kintyre and have been told of a good source in the Cumbrian Fells that I've yet to visit.
I dare say your local head shop will have a tub of pebbles that you could rummage through.

Here's some bumf on rock crystal:
http://www.mineralminers.com/html/quaminfo.htm
http://23.1911encyclopedia.org/R/RO/ROCK_CRYSTAL.htm

Haven't tried it myself(it's on the to-do-someday list) but I've ground a couple of blades from stone and was surprised how quick it goes once you find the right grinding stone material.
A sheet of wet and dry in the bottom of a wok(with a round bottom) gives a nice curve for finishing up, not very primitive I know but hey, it works.

 

[jdlenton]

If I remember correctly Galileo made his own telescope in the 13th century (think I got the time right please correct if not) using glass he ground and polished with not much more than blocks of wood carved with the correct curvature required for the lenses surface and various grades of grinding compound and polishes ( don’t know what he used but back then you can bet they where all natural .



I’ve done a bit of glass work don’t quote me but glass begins to melt at about 1100 degrees C so you could melt and cast glass in a charcoal fired kiln but boy yopu’d need to pump the bellows for along time to get up to that temperature



The next problem is impurities form the fire don’t know much about this would take some experimenting.



Happy glass making



James

 

[Grooveski]

These pages have photos of crystal lenses. There's another page somewhere with shots of those discovered at Troy but I can't find it again.

http://www.vikinganswerlady.com/fire.htm
http://www.arkeodok.com/excreport1.2004.html

 

[JohnC]

I've had a plan (never got round to it yet) of taking a silvered survival blanket, stretching it over a large pot and removing some of the air from the pot, ?with a tube tucked down the side, to make a concave mirror to focus the sun.
As I say, it's a plan. One of these days......

 

[rich59]

I presume the bellows are intended to increase the air flow to allow more burning. I guess a good chimney arrangement would help as well to draw air through.

If I was to melt some glass I suspect I would need a mould to form the shape of a lens. That would ideally be of a fireproof but shapable material, maybe clay?

 

[stevec]

it might be of interest to find the OU rough science website, IIRC the women physicist made a lens or two. i'll have a quick trawl and find the site
sc

nope i'm having trouble finding it.i seem to recall that it was series two, i think she used a rod of soda glass, which melts a lot lower than borosilicate(pyrex) she put the rod in the hot part of the fire and twiddled it forwant of a more accurate description!
i made a spherical lens in a similar way by melting the end of a pippette. i seem to recall that the first microscope had a similar spherical lens.
sorry not to be more help
sc

 

[jdlenton]

glass blowers use soaked wood to shape the glass

 

[AJB]

John C, I would be interested in your results from that, in the field, the top of a cooking pot doesn’t have that much smaller diameter than the bucket, I wonder if it would have the resolving power to ignite tinder at the focus?

As to the tube, I bet if you filled the bucket/pot with boiling water for a few minutes, empted it, and then sealed it with the blanket; the atmosphere would do the rest as it cooled, no need for a pump.

Rich, I’m sure this won’t help much, as it would take forever, but I’m sure I remember my dad, a physicist, saying years ago, that if you rub two flattish lumps of glass together, with a circular motion, they will naturally form a convex and concaved pair of lenses.

Let us know how you get on.

Andy

 

[JohnC]

Could a bowdrill be adapted to provide the spin to grind a piece of crystal against a depression on another rock?

I have seen a pic of a (clear) light bulb containing water used as a lens.

I believe a clear glass globe filled with water was used in the past as a magnifier/light intensifier in libraries.

 

[rich59]

You guys are so full of ideas. Thanks. I can't possibly check all that out in the next few weeks. I think I will look at creating hot fires in the near future.

I will look into shaping and polishing glass.

Would chocolate be useful as a polisher? I note this in the coke can thread. Why chocolate?

The concept of rubbing down glass with a hand drill is fab.

 

[JohnC]

I got the impression that chocolate was used because it was there, has a fine particle makeup that allowed polishing. Toothpaste or brasso would do the same. Liek most polishing, you start off with a coarse grind then get progressively finer.

 

[rich59]

Making a fire hot enough to melt glass - just had a memory of going round a glass factory. For small work like bending a glass rod they would simply put it into a hot blue flame like a bunsen burner at school.

The difference between the flame that comes from burning wood (yellow) and a hot blue flame (e.g. bunsen burner, blow lamp, kitchen gas ring) is the air / gas mix. Therefore is may be possible to get a hot blue flame from ordinary wood.

First one must be able to control/ focus the gas coming off the burning wood. An example of this is when one makes char cloth. Put your material - be it cloth or wood or whatever in a closed tin with a hole and put it on the fire. Once it is hot you get a jet of gases that ignite and burn quite excitingly in a jet of flame.

So, now all I have to do if figure on the best configuration to get a good gas/ air mix before it comes out of the hole. It should probably not be under pressure, so a larger outlet hole would be good. Then I probably need a hole in the bottom or sides to draw in air. But then air around a fire is probably a bit starved of oxygen so better to get air input from an axtra source such as bellows. Also air coming into the tin would simply allow the wood in it to burn normally. So, I need the gas to leave the wood before adding the air. I see a tin with a bunsen burner sitting on top in my mind's eye.

I'll work on this. Has anyone else any thoughts or experience on burning hotly the gases coming off burning wood?

 

[Roving Rich]

We melted glass bottles in the fire in the roundhouse at the first Wilderness gathering - all you need a really really hot fire - when the core ir glowing white hot, you have plenty of heat there. I met a firewalker who would test his fires like that, see what they would melt, aluminium, glass etc.
I'm still not convinced how you would shape it ? Clay might work - it gets used for casting bronze.
A friend claims a friend of his (mathematist and astrologer - mad proffessor type) set about making his own telescope. He used optical glass an ground it down with various grits, finishing it off with Jewelers rouge. Twenty strokes, turn it somany dgress twenty strokes.... took him years apparently.
Mayby a mirror would be easier to make ?
What are yuo looking at usung it for ?
Cheers
Rich

 

[Joules]

Look up glass slumping (heating glass over a former) to shape it. Could be used to make a lense oil/water filled ??? or as suggested a focal mirror...


Joules

 

[Ogri the trog]

Jon,
Your idea of a parabolic relfector is just so simple. I really like that, let us know how you get on - all it would do here is collect rain today!

I really must give it a go myself sometime.

ATB

Ogri the trog

 

[JohnC]

It's raining in Edinburgh.