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Fotoguy20d
4-Aug-2011, 13:27
I have a Gundlach rapid rectilinear (3 cemented glasses), around 1.5" diameter, soaking in acetone as I type this. In under an hour, I already see a yellowing band around 1/4" forming on the perimeter. Any idea how long it should take before the acetone gets through all the balsam? How long do I need to leave the lenses sitting there soaking? Will the acetone dissolve all the balsam or will I need to peel the lenses apart? How do I clean them off? What are the handling precautions for the acetone? Anything else I should know? Where do I get something to glue the glass back together when it's clean?

Thanks,
Dan

goamules
4-Aug-2011, 14:09
Ha! You're asking a lot of questions for already having the lens soaking in it!

Here are some more:
- Is acetone explosive?
- Can you drink it?
- Will my lens be more valuable with half the lens separated?
- Should I use the dog water bowl for soaking?

Just funnin ya.

Fotoguy20d
4-Aug-2011, 14:12
Always jump in with both feet...

In order:

Yes (or at least very very flammable)
Yes (you can, technically. should you drink it - no!)
Yes (you should have seen it before I started, and, I cut off the peened over brass long ago)
Yes (I don't have a dog and my neighbor's dog is a yappy little thing)

:)

Curt Palm
4-Aug-2011, 14:36
Always jump in with both feet...



Hopefully not into the acetone!

rdenney
4-Aug-2011, 14:44
Hopefully not into the acetone!

If my wife can use it to remove nail polish, it must not be that bad. She's sensitive to a range of chemical smells but the acetone doesn't seem to bother her. It drives me out of the house!

Rick "who has a couple of gallons in the garage, however" Denney

Jim Fitzgerald
4-Aug-2011, 14:59
"I love the smell of acetone, it means carbon printing!" I have gallons of it also. Acetone is fun, but I always have a fan on it!!

John Jarosz
4-Aug-2011, 15:11
Did you mark the orientation of the two elements with respect to each other?

John Jarosz
4-Aug-2011, 15:13
Norland Optical Cement (http://www.norlandprod.com/adhesives/noa%2060.html)

James E Galvin
4-Aug-2011, 15:20
I have usually used MEK. It may take a couple of weeks. When done, the elements will slide apart, maybe slowly since the balsam is not gone yet, just softened. Clean up with the acetone and a soft tissue or soft cloth. You need to get the glass very clean.
Re-cement with UV curing epoxy, available from Edmund Scientific Co. You will need to make a fixture to hold the elements aligned, for a lens that size I have used 3 pieces of microscope slide and a rubber band. It is helpful to tape the slide pieces together so that the 3 can be handled with one hand while you adjust the rubber band. Put a drop of the epoxy on one element, place the other on top. After a while the epoxy will flow to the edges. Press down. If there are bubbles and dirt, redo. The epoxy doesn't start to cure until exposed to UV, so there is no rush.
With the elements well aligned, expose to UV for (a UV fluorescent lamp works) for a few minutes. The epoxy is now set, but still soft enough to easily clean up with a tissue moistened with the acetone, or take back apart with a short soak in acetone. Now give an hour or two exposure. Done.

Merg Ross
4-Aug-2011, 15:23
"I love the smell of acetone.....!"

Me too! Metol/Acetone film developer is my favorite for large format.

Steven Tribe
4-Aug-2011, 15:27
Can take up to a week. The line of solution moves slower when it gets past the discoloured layer.
The sticky remains of the balsam will still be on both internal faces when it loosens.
Canada Balsam is still available.
Think carefully about the reglueing sequence - don't try and fix the two joins in the three lens achromatic at the same time!

Jim Galli
4-Aug-2011, 15:42
Did you know a drop of Wesson Oil between the elements can serve optically as a temporary substitute for re-cementing. Not very permanent, but I've got images taken with a petzval that front element was temped with wesson oil. Optically it seemed to work fine. Might have lasted for years, who knows.

Drew Wiley
4-Aug-2011, 15:44
Actone is fun stuff. About twenty years ago there was a paint mfg about three blocks
down the railroad track from here. One day every building around was rattled like crazy by a horrific blast. A tank car of acetone had become totally vaporized and they
never found the workman who was pumping it - apparently completely vaporized too -
but they did find his cigarette lighter laying intact right beside the railroad track.

Vaughn
4-Aug-2011, 15:58
If my wife can use it to remove nail polish, it must not be that bad. She's sensitive to a range of chemical smells but the acetone doesn't seem to bother her. It drives me out of the house!

Rick "who has a couple of gallons in the garage, however" Denney

Yeah -- and I found the paint on the bathroom vanity getting soft. Somehow, it was never her fault...

In carbon printing one can use rubbing alcohol (isopropyl) or acetone for spirit sensitizing. I prefer acetone for several reasons -- a minor one being that the smell of rubbing alcohol reminds me of the many times I was sick as a kid and my mom would pour some on my back in attempts to lower my body temperature (often peaking at 104 to 105F).

Good luck in your lens project! Way to jump into it with both feet!

Vaughn

Drew Wiley
4-Aug-2011, 16:14
Nail polish remover is mostly acetone, but what is contained in nail polish itself would be illegal to sell in a paint store. It's basically a category of lacquer considered too dangerous for industrial use and is officially the very biggest source of toxic contamination in landfills! The cosmetics industry apparently has the influence money to fly under the radar. Lacquer solvents go right thru the skin into the bloodstream, unlike acetone which simply dries the skin out and causes it to itch. A known carcinogen too. That's why I substitute acetone for lacquer thinner whenever possible.
Might as well be sniffing glue. One of the local ambulance drivers was telling me about
how many women he had to ressucitate or defibrillate every month in nail parlors.

Fotoguy20d
4-Aug-2011, 16:15
I did mark the glass in pencil - two places, about 120 degrees apart so I won't get confused later. Thanks for the cement links - is 3cc enough or do I need the 1 oz bottle (in which case I'll play with a couple of ugly bausch lenses I have).

I wish I had taken a photo of the cemented set before it went into the bath (in an old tomato sauce jar by the way) - I've never seen anything that ugly. I have a feeling it was separating and someone tried to reflow it.

The lens is an 8x10 Gundlach Rapid Rectigraph - 13", 20 1/2", 29", in a badly pitted worn brass barrel. It's probably not worth all this effort but its a good learning experience.

Dan

James E Galvin
5-Aug-2011, 06:25
I have not worried about the relative rotation. 3cc is enough for many lenses, you only need 1 drop.

Tim Deming
5-Aug-2011, 08:58
I tried using acetone, and then toluene, to "unglue" a badly separated doublet. After about a week and little progress (it was a 3" dia doublet), I changed tack and put the doublet in the oven. The balsam was soft enough in about 30 min to slide the elements apart easily. Clean up with acetone after that was a snap and I was ready to re-cement. I find this much easier than waiting for the slow diffusion of solvent into old balsam.

I use Canada balsam to re-cement since it is very forgiving, is easily removable, and has given me good results.

A few hints if you want to try this. Put the lens on something soft in the cold oven (I used a silicone potholder). Then heat up the oven with lens inside, this will allow the lens to slowly come up to temperature (I would not risk putting a room temp lens directly into a hot oven due to possible thermal shock). I used 275 deg F. Afer ~30 min, I grabbed the elements using newspaper ovenmitts, and was able to slide them apart. Then let them cool slowly on a small stack of newspaper. You will get a nice "pine forest" smell in your oven from the balsam, but I do prefer that to organic solvents. Of course, this method wont work for modern cemented lenses where balsam was not used.

cheers

Tim

John Schneider
5-Aug-2011, 21:36
Acetone is almost non-toxic (no. 1 for toxicity on the NFPA diamond); it's produced by the body during fasting and during pregnancy, when the added energy that metabolic pathway provides is needed). It is flammable as all get-out, however. Toluene is a ton more toxic and is a suspected carcinogen (the only reason it has any industrial uses is that it's still safer than benzene).

I did try decementing my first lens by soaking in xylene, but eventually gave up and used the oven. That worked superbly.

Fotoguy20d
6-Aug-2011, 11:13
The thin back piece of glass is off (it did indeed just slip off on its own), wiped clean and sitting on the side already. The other two are moving along more slowly (I suspect most of the separation was with the thin one). If they come apart before the week is out, I'm going to try Jim's oil idea (how will olive oil work?) so I can use the lens at an event next weekend.

Dan

erie patsellis
6-Aug-2011, 13:18
I use turbine oil, it takes a few days for it to wick in, only start at one spot though, as you can trap air and it will be a pain to get it out. If you want it to be semi permanent, after the oil has wicked in, clean the edges of the elements and lightly paint them with some lacquer over the seam, seals the oil in and works like a charm.

Fotoguy20d
7-Aug-2011, 11:55
I don't know if it was the condition of the balsam in this lens, or the heat outside, but the last two pieces of glass are now separated. Took a bit of wiping with acetone to get the glass completely clean but its amazing how well hundred year old glass can clean up. I dropped all three pieces back into their brass fitting, but, since I milled off the peened over bit to get them out, there's nothing to keep them there. Ultimately, I was thinking of either painting them into place, or maybe a couple dabs of epoxy between glass and brass, but I don't want to do that until they're cemented together. I haven't even ordered adhesive yet since I expected this to take much longer.

As an interesting aside, I have an aperture-less Betax #4 which has step down rings both front and back. Below the female thread, there's a step in the brass, of smaller diameter than the thread. Playing with it a few days ago, it turns out to be a near perfect match to the diameter of the rear cell of this Gundlach lens. A little gaffers tape (maybe even too thick) and it'll be a very snug friction fit. Even without, the lens can be suspended vertically from the shutter and remain in place. So, this junker lens is now not only close to being up and running, it's close to having a shutter as well. Now to cut some waterhouse stops for it...

Dan

Steven Tribe
7-Aug-2011, 13:57
The Rectigraph had/has a good reputation.
Now that the acetone is well into the other balsam join, it might be worthwhile to warm it up for a short time (less than 100 deg C) and then see if you can move the two lenses relative to each other.
I find that rotation is a less stressful motion than pushing down on one side!
Didn't see your last entry!

Fotoguy20d
8-Aug-2011, 05:43
I've been doing my research going through the archives here.

NOA60 (http://www.edmundoptics.com/products/displayproduct.cfm?productid=1597) or a chunk of balsam (http://www.surplusshed.com/pages/item/b1077.html)? Would this work (http://www.naturalpigments.com/detail.asp?PRODUCT_ID=510-33CAN04)?

Dan

Fotoguy20d
8-Aug-2011, 05:45
Or maybe this (http://shop2.chemassociates.com/PAS-balsam.html#2069)?

Dan

BarryS
8-Aug-2011, 07:06
Those are all fine. I got mine here (http://www.artcraftchemicals.com/products/products-page/general-chemistry/a-m/canadian-balsam-fir-part-1656/).

Fotoguy20d
8-Aug-2011, 07:15
Those are all fine. I got mine here (http://www.artcraftchemicals.com/products/products-page/general-chemistry/a-m/canadian-balsam-fir-part-1656/).

Is it a liquid or a solid? Liquid seems preferable since I don't have xylene and would prefer not to have to buy a pint. Does the liquid need to be diluted anyway? Is there a drawback to liquid form over the chunk from surplus shed? I'm leaning towards balsam for ease of rework.

Jay DeFehr
8-Aug-2011, 08:04
You've inspired me! I have a 7-1/2" lens with a wide aperture (don't remember the specifics) I bought for a few dollars because I liked the FL/aperture combo. It arrived in terrible shape, and after peering through it, I lost interest. I was looking at a site dedicated to telescope optics, and there is a good write up about lens grinding/polishing, and it recommends the vegetable oil method for joining elements. I think I'll have a go at polishing and re-cementing my junker. Thanks for the nudge!

Steven Tribe
8-Aug-2011, 08:26
The small liquid bottles of fresh balsam are recommended.
UV glue has very restricted shelf life, whilst canada balsam, away from the light, keeps for ever. It will thicken slightly if you don't seal the lid too well, but a small amount of zylene will bring it back to a sirup consistency.

Fotoguy20d
8-Aug-2011, 08:33
So how do I get the liquid balsam to cure? What is the balsam suspended in?

Dan

Fotoguy20d
8-Aug-2011, 08:46
Thanks to all the advice and help everyone's been providing. Here's the lens mounted on my 2-D yesterday afternoon. The rear is the damaged element but it wouldn't be obvious anymore on casual examination.

I shot through the complete lens with the rear elements, no oil between them, taped loosely in place with some black tape on the edge. Image was a bit soft, not surprising perhaps since the rear glass is not up to spec, and the lens was wide open, but, I think it'll be fun to shoot with once recemented. I also think the opening in the betax is not large enough for the lens and there was some vignetting. All in all, this has been a fun project and good learning experience, and I'm looking forward to the outcome. Went looking around the house for other separated lenses yesterday - only found a 5x7 B&L Planatograph so far.

Dan

Steven Tribe
8-Aug-2011, 10:06
The light fractions in liquid (thick/sticky) balsam evaporate very quickly. A couple of hours in the oven at about 50 deg C will be enough to set the balsam once the join has been made and checked.
There is a thread here about rebalsaming - and there are other guides online.
Fresh Canade balsam does have a slight greenish tinge.

Robert Hughes
9-Aug-2011, 11:29
I'm surprised that EPA considers acetone to be relatively non-toxic. When I was a kid I was told it rots brain cells on contact, and I always had to use a respirator around it.

E. von Hoegh
9-Aug-2011, 12:51
You can run a lawnmower on acetone. (Also kerosene, turpentine, jet-A, isopropyl alcohlol, Everclear, and a few others) But it dissolves things in the carburettor.

Sevo
9-Aug-2011, 13:18
I'm surprised that EPA considers acetone to be relatively non-toxic. When I was a kid I was told it rots brain cells on contact, and I always had to use a respirator around it.

Never trust the things you were told as a kid... Acetone indeed is slightly less toxic than alcohol.

Fotoguy20d
12-Aug-2011, 10:46
My bottle of canadian balsam is in hand (looks like very viscous maple syrup). I've read through Steven's wonderful instructions (http://www.largeformatphotography.info/forum/showthread.php?t=58763&) on how to cerement a lens. My lens is not a doublet but a triplet (thanks Gundlach) - will reheating the cemented pair to add the third glass damage the first balsam joint?

Dan

E. von Hoegh
12-Aug-2011, 11:15
My bottle of canadian balsam is in hand (looks like very viscous maple syrup). I've read through Steven's wonderful instructions (http://www.largeformatphotography.info/forum/showthread.php?t=58763&) on how to cerement a lens. My lens is not a doublet but a triplet (thanks Gundlach) - will reheating the cemented pair to add the third glass damage the first balsam joint?

Dan

Cement all three at once using v-blocks to align them.

Steven Tribe
14-Aug-2011, 14:02
If you do a double process then you can first produce a doublet with a convex face for the second glueing. You only have to warm the remaining glass, remove it quickly, add the next blob of balsam on the warm concave side (smart!) and apply the convex side of the already finished doublet (which doesn't have to be heated - or just a little) and push the balsam out to the edges.

My experience tells me that a double layer can't been effectively with balsam in one go. Seeping balsam becomes a real problem for using fingers effectively and it is difficult to control for bubbles and specks. And you only have a few minutes before the glass cools and the balsam thickens.

The V block system sounds good, but most of the balsam jobs I have done have been
with achromats where the upper glass has a smaller diameter than the other glass. This helps rough allignment, though. I use a spot light/conciding reflections for allignment.

Sorry this is a bit delayed. Canada Balsam is the same product as maple syrup - just from different trees!

Fotoguy20d
17-Aug-2011, 08:24
First pair was cleaned, heated to somewhere around 50-60C (since I could just briefly touch it), and a small drop of balsam applied to the concave surface of one element using the back of my darkroom thermometer (the only glass rod I could find). Squeezed, and had a beautiful, bubble free, well filled bond line. Except for the one tiny black fleck of something that is. So, an acetone bath later, followed by more cleaning, re-heating, etc, the first pair is now cooling in the kitchen. What do I need to do to cure the adhesive? How long before I try attaching the third glass?

Thanks,
Dan

Steven Tribe
17-Aug-2011, 11:04
As long as it was heated at around 50 deg C for an hour or so and has cooled down - any time!
You don't have to heat the doublet again - just warm the single remaining lens.
Did you get sticky fingers?

Fotoguy20d
17-Aug-2011, 11:10
Very sticky. I washed in acetone - nothing else seems to want to clean it up. The cemented trio is now sitting outside (its around 30C here) hopefully setting up nicely. Once that's done, I figure on very carefully wiping the outside surfaces with acetone to remove the balsamic fingerprints. Then, to figure out how to replace it in its mount, which had the burnished edge removed - I'm thinking of trying a bit of black paint around the glass edge and then putting it into the mount wet. Otherwise, a couple of small dabs of black epoxy between chamfered glass edge and brass mount.

Dan

Steven Tribe
17-Aug-2011, 11:50
Most of mine with the burnished edge were such a close fit that I used Canada balsam (surprise!) to lock the down. They are still OK after a few years!
Mat black paint ( water based ), which has half dried out, might be better.

Drew Wiley
17-Aug-2011, 12:10
Balsam is a natural resin and a very low tech approach to cementing lenses, but not as
primitive as shellac. Given enough time and balsam cures into amber. You can watch it
happening if you live fifty million years. But guess what the Hubble telescope lenses are
cemented into place with? Old-fashioned bug shellac. How do I know? I sold it to them!

Michael Clark
17-Aug-2011, 12:46
What is BUG shellac and what are the reasons for using it in outer space on such a high tech instrument as Hubble.

Fotoguy20d
17-Aug-2011, 13:05
I hope it doesn't outgas.

Michael Clark
17-Aug-2011, 13:06
Here is what I found http://www.shellac-india.com/about-shellac.htm pretty primitive stuff for a telescope in orbit around earth.

Mike

Fotoguy20d
17-Aug-2011, 13:09
As long as it doesn't outgas and leave deposits on the glass, the ideal material is probably one that is flexible and has a good coefficient of expansion match to the materials it's bonding.

Drew Wiley
17-Aug-2011, 13:26
Shellac was the very first lens cement. It's the sticky weatherizing lac of aphid or
mealy-bug like insects left on limbs in certain tropical countries - keeps them dry in
the rainy season and prevents them drying out in the dry season. Traditional woodworkers know what this stuff is. It spreads easily and dries quickly. One would use a very clear bleached grade for lenses, that is, is your name is Galileo and you don't know of anything better. But it makes perfect sense for mounting real big lenses for space. What causes shellac to fail is long-term crosslinking from oxidation, and you don't have that problem in space. UV might also be an issue, but the Hubble wasn't designed to last more than a few decades. Canada balsam is comparatively messy
and hard to acquire in large quanitites. Nowadays it is still sometimes used for
embedding specimens in microscope-slide wells.