How I did it: new balsam for a sick RR

[Steven Tribe]

THIS THREAD IS CURRENTLY WITHOUT THE PHOTOS I UPLOADED AT THE TIME DUE TO AN OUTAGE SOME TIME AGO. I NO LONGER HAVE THE IMAGES FROM 2011. SO UNLESS THERE IS A MIRACLE AT LFPF, IT WILL REMAIN PRETTY MUCH WITHOUT VALUE! SORRY! April 2017.




The job has actually been completed and I will post photos, explain what went well - and badly - along with text and diagrams over the next week or so. I have done this before - mostly with modern UV glues - but this time I have experimented a little to find out "the most foolproof method". Please don't let this be one way communication -and I don't claim to have discovered "the method". But perhaps if you restricted contributions to the step I am describing it would make the whole more logical for those who join later.

The candidate for rejuvenation is a Suter Aplanat A No. 4. A nice big extra rapid RR.
This first picture is what the front cell looked like after removal from the mount. This is cheating a bit - but the yellowing is more obvious out of the mount. Apart from the discoloured ring, there were much larger areas of colourless separation well towards the centre. The rear cell was in perfect condition.

[Scott Davis]

Steven-

I would be very happy to hear full details (or even better, see a YouTube video??? hint hint!) of this process, as I have a lens or two that could benefit as well.

[Steven Tribe]

This first balsam replacement (there are two others underway) is probably the easiest as Suter used a system of mounting the cemented lens which was designed for servicing. The classic book on objective construction shows a slightly less sensible system (photo 1). I think the thickness of the brass edge to be "turned down" over the lens has been exagerated for the purpose of illustration - I would guess that something made like this would be capable of being "rolled back" with hand tools.
The Suter mount is photo 2. This looked quite formidable as the ring was obviously a separate piece of brass. But it could have had a rim at 90 degrees which acted as a spacer between the side of the lens and the interior wall of the cell mount.
Lifting the paperthin edge of the mount, which had only a 1mm overlap, showed the construction to be fortunately as figure 3 (no artist here!). This done using a hobby knife blade to get it started and then a suitable piece of hardwood (boxwood is tradition but I had to settle for walnut). Note that Suter's made a sloping edge on the loose rim to make things easy.
If the cementing edge had been at the side, rather than the top, the lens pair might have been difficult to remove, as I suspect some makers used excess balsam to "fix" their lenses in position. Or seeping balsam has run out and hardened.

[Steven Tribe]

I think the glueing might be a suitable candidate for YouTube - but I'll try and illustrate that process as well as I can here (if you stand my sketches). There is a very real problem of sticky fingers which is unavoidable in the process and seconds count.

[BrianShaw]

I think the thickness of the brass edge to be "turned down" over the lens has been exagerated for the purpose of illustration - I would guess that something made like this would be capable of being "rolled back" with hand tools.

Maybe worth a try. But my experience in clock/watch and other types of repair is that more often than not the brass has been sufficiently "work hardened" by the original peening/turning that it won't roll back without a fight or breaking. My personal experience includes trying this and ending up with stab wounds in my hand or damaged (insert name of thing being fixed). Maybe if it were chucked in a lathe it could be coaxed to roll back just one more time... I don't know, but suspect if that were the case the "classic texts" would have mentioned that option. Cutting the rolled-over part might be more expedient. All that being said, I've never tried this kind of work on an antique lens.

This is very interesting; please keep documenting your progress!

[Steven Tribe]

In all the period instructions it says "mount the brass lens in a boxwood chuck on a lathe and turn back the brass rim". The first sketch from Orford's "Lens work for Amateurs" shows an edge that I would remove rather than try and lift back. The third objective I am working on, does require a cut out and a new "fixing" system. The turnback edge of the Suter was almost foil thickness.

[Steven Tribe]

I have done a quick check of my old brassies with non-screw lens mounts.

The "Suter" system seems quite popular - a bendable brass foil edge turned down about a 1mm. The lens edge has, in some instances, been ground down to form a curve to accept the retaining brass. The only "solid" turned over edge is on the "Anon." large rectilinear I have up for repair. There is just a chance that this is really a flat rim with an edge at 90 degrees which was been pressed into the barrel. Whatever the structure - it will still have to be cut out.

There is another type I haven't noticed before. Here the lens appears to have a pressure brass ring forced into the barrel opening. It looks rather like the system used to make the light-tight reduction flanges in objectives with Waterhouse slots. Next posting will be about Canada Balsam and Zylene/Zylol.

[Steven Tribe]

Canada balsam is a natural product product like maple syrup and latex. Unlike wine, there doesn't appear to many differences between the various vintages of Canada Balsam. The basic material is quite uniform. The problem starts with the purpose to which the balsam is put. Some applications require a thin material whilst others, including lens cementing, require the natural state balsam. The standard thinning solvent used, and which is also used for removing excess, is Zylol/Zylene. This is a very nasty solvent ,healthwise - and at minumum will give you, or some other member of your household, a headache within half-an-hour.

Zylene/Zylol has the additional role of gradually dissolving the aged balsam in the join.
Canada Balsam is used as it has approximately the same refractive index as the commonly used "old" type glass - 1.54. The reasons it is still used are:

1. It is comparitively cheap compared with modern (UV hardening) optical glues.

2. The big problem with UV cured synthetics is their very short shelf lives. Although they contain as much as the 15ml Balsam (1 oz) there is no way that you use more than just a fraction unless you are starting a recementing business. Expiry date is 9 months after manufacturing date. I do not have personal experience of the real shelf life of canada balsam, but would suggest it is indefinite if stored in a cool and dark place. Certainly the lenses I have separated - over a hundred years old - still have large areas which appear to be identical in all features (including a distinct smell/aroma) to the new balsam I have been working with.

Zylene/Zylol is a standard product available locally. Canada Balsam is more problematic because the "mix" of the product appears to vary according to the end use. There has been an e**y provider from Quebec (sounds perfect!) but he/she has gone "belly-up". There is another source in the UK at the moment. The product we are after is the same as that used for geological slides in microscopy - this market is many times bigger than ours.

I would be grateful for extra/contrary comments from those who have had long term experience with Canada Balsam. Additional sources/shelf life/quality issues?

How to work with balsam and general properties of balsam will come under the recementing section.

Next time - Separating the lenses.

[Steven Tribe]

No. This is more about the alternative UV glue. I did a successful recementing with the UV glue a couple of years ago. There may be some of you who don't like the idea of using a very sticky and smelly material which balsam definitely is. I have just retrieved the old instructions and 98% full bottle from 2 years ago. I would say that the glue is still useable - it has the same consistency as 2 years ago. I also note that Norland say " has a minimum shelf life of six months. I thought the technical data might be useful as it contains more than on their website.
I have often seen that this a more "permanent" cementing than balsam. But they can be split quite easily with methylene chloride (carefull - a wicked solvent).

[Steven Tribe]

Separation

First of all, temperatures noted in these next sections all Centigrade/Celsius and all work must be done with forced ventillation or outside!

The first point is about heating the cemented combination as a method of separation. I have read that "leaving the objective in the sun" is a cause of the delamination and that the "balsam can be softened by heating and the two lenses can be separated". Whilst the first may be true to some extent but I doubt whether the second is. When the lens has been rebalsamed, the balsam is "baked" for a few hours at 100 degrees. It may be that, at higher temperatures, there is some degree of loosening - but that would involve difficult handling of the lens surfaces and increased risk of glass heat damage.

So the method I found most successful and safe after trying out various methods was a simple long term soak in xylene. Total time was about a week on average.
This aplanat delamination was a combination of the serious edge degradation and a central "hole" with a channel to the edge.

The first photo shows the layout of the soak. Nothing high technological here. It is not necessary with much solvent as the capillary forces at work are much more important than a "header" of solvent. A small as possible hard thermoplastic, sealable, container. Small size reduces the use of solvent and reduces the amount of released vapours when you make your inspection of progress! A white container has advantages.

Photo 2 shows the various stages in the soak. The first figure show the starting point with a central clear delamination and the typical edge breakdown. The colour of this approaches brown and usual has a blotchy/mottled appearance.

Not much seems to happen the first few days. But you may note that the colour of the edge become more uniform and the boundary between the delamination and the uneffected balsam becomes more distinct. The central delamination was uneffected at this stage.
After a few more days, the solvent will be noticably colored and the edge lamination will be much paler as well. Don't be alarmed at the apparently slow inward march of the phase line showing the progress of the dissolving process. The speed starts at about 1 mm per 24 hours once the solvent has reached the edge of the delamination. At this stage I have changed the solvent in order to be able to monitor progress without taking the lens up (works only if you have a white container!). Photo 3 shows this stage - note the brownish clump which suddenly appear in the solvent.

In the final phase (stage IV), there is not longer any difference between the edge and central clear delamination. The gradual loss of colour makes it difficult to spot the edge. A separation should be possible at this stage.
It is easy to forget that the insert glass has very thin edges so I have always attempted to turn the glass, rather than push to one side. Be prepared for a very sticky inside surface and a quite delicate lens. The strange thing is the smell - which is exactly the same as the fresh canada balsam you already know. A short section on cleaning/preparation will follow very soon.

[Steven Tribe]

CLEANING AFTER SEPARATION

The two component lenses (flint and crown) will look very messy after this separation. The small amount of balsam used is enough to create a very lumpy appearance. The cleaning may have two stage as there can be edge deposits which are not soluble. Using protective gloves, take the lens up and clean with xylene impregnated paper towels. The deposit does not come away from the surface easily and mechanical rubbing is necessary to get it on the paper. Throw away the papers quite quickly as you soon reach the stage where you put more back on than you remove with each stroke. The quality of the cleaning papers should increase as you get near the surface.

You may discover a whitish deposit at the very edge. I have no idea what this is (perhaps sugar?) but must be a result of the decomposition of the complex mixture which balsam is. To be honest, I loosened this with my finger nail edge.
I enclose photos which show the general appearance of the crown/flint set, both before and after cleaning. The white edge is also shown.

Hope someone is finding this account useful or amusing!

[eddie]

Hope someone is finding this account useful or amusing!

i am ! i have a soft spot for Suter lenses. i have several. i love them. i would like to see yours. i have the series B #6 and #8 (early serial numbers) and a petzval that are my favorites.

if you need more practice i have some lenses to send you....LOL :)

eddie

Edit: to add the picture of my baby....

[imagedowser]

I understand it is a good idea to mark the edge of the lens being separated with two light marks at 90 deg to each other on the edge, with a fine sharpening stone, to make it possible to re-register the lens in it's orig. alignment during re-cementing. Is this necessary?

[rguinter]

Zylene/Zylol is a standard product available locally.

Steven: Don't forget that the Zylene you are describing (yes it is a good solvent) is spelled with an "X" in the US: i.e., Xylene.

If one goes looking for Zylene here there will be confusion. Bob G.

[rguinter]

But they can be split quite easily with methylene chloride (carefull - a wicked solvent).

The good news with methylene chloride is that it is so irritating that one is not likely to work with it for long voluntarily and be badly exposed.

The bad news is that carboxyhemoglobin and formaldehyde are produced in the body as it metabolizes and formaldehyde is a carcinogen. i.e., as a result methylene chloride (a.k.a., dichloromethane) is also considered to be carcinogenic.

Further bad news is its vapor pressure is so high that it tends to go right through standard respirator cartridges very quickly.

My advice; If you decide to use it make sure there is excellent ventilation to keep the vapors out of your breathing zone.

Regards. Bob G.

[Steven Tribe]

Thanks for the feedback!

Xylol/Xylene is spelt that way here, too! Sorry about the careless slip!

"I understand it is a good idea to mark the edge of the lens being separated with two light marks at 90 deg to each other on the edge, with a fine sharpening stone, to make it possible to re-register the lens in it's orig. alignment during re-cementing. Is this necessary?" No, the lens are spherically gound/polished so there should be no problem with allignment at 13, 79 or 271 etc. degrees to the original glue position which was quite random. More useful would be micrometer measures of the distance from the edges of the flint to the crown and the distance the flint sticks up above the surface of the crown. I tried but found the job beyond my skills with a micrometer. There is good reason to believe that a pair suffering from separation no longer has the original orientation.
I have decided to enclose a later section about optically checking the success of the
positioning of the lenses.

[Steven Tribe]

I am not sure how easily methylene chloride (CH2Cl2) is available anymore. It used to be the active component in really effective paint removers. Perhaps "wicked" was an understatement. The commericial product was rather gel like so there was time enough to place a dollop in a glass container (not plastic here) close the lid and retreat quickly inside.

[IanG]

Well paint stripper is still available in the UK, that's mainly methylene chloride.

Ian

[Steven Tribe]

PROPERTIES OF CANADA BALSAM AND HOW TO GET IT ONTO THE CONCAVE SURFACE.

This section is based on a period of about eight, mostly very unsuccesful, attempts. I followed the recommended procedures as well as trying out thinning the balsam. This series of experiments was mostly to get a methods which avoided air bubbles. In summary, Both lenses need to be warm, the balsam cool and the balsam needs to be "melted" into the centre.

Proper balsam is stiff and will only just "pour" or "fall" out of its container. It has a very strong aroma which is about as dangerous as walking past a row of freshly felled trees! In the container, there are no signs of air bubbles. However, once formed, they stay there for a long time.

Attempts to use a small quantity of xylene thinner (less than 5%) produced a more rapidly flowing substance - with few air bubbles - which allowed a succesful bond with cold lenses. Unfortunately, a permanent haze appeared throughout the cement layer.
Conclusion: use Canada Balsam and warm lenses.

I began to realise that the first application of the balsam is crucial. The wrongly applied balsam, even on warm concave surfaces, produces quite a few air bubbles. Photo 1 shows the typical results of wrong application. The amount deposited is much more than necessary!

The way to apply the balsam is to facilitate a direct physical contact between the hot lens and the balsam so that the balsam warms instantly and seeps down onto the lens. I have tried this with both the container itself and a thickish (5mm - 10mm) glass rod. It takes just a few seconds for this to allow enough balsam to spread out in the centre. Working with a pipette or allowing drops to fall from the container doesn't seem to work at all (Photo 2).

[Graham Patterson]

My only experience with Canada Balsam is for making geological sections. You need to cook it enough so it hardens, but not so much that it discolours. According to my lab reference for geological section making, around 3 minutes at 85C would do it. This is for low mas items like 3x1 microscope slides and small blocks of rock. The usual test was to pick up a small bead on a mounting needle and see if it hardened when it cooled.

Air bubbles can be led to the edge with a needle while the cement is fluid. The trick is to let the balsam flow. Trying to stir it or push it tends to add bubbles. Making sections we could push bubbles ahead of the specimen by lowering on one edge first and then forcing out the cement. Again, not something that will work with curved lens surfaces, though capillary action should help.

We used a lot of thermoplastic mounting medium (Lakeside 70C) because it was a) cheaper, and b) did not need to be cured so precisely (both good qualities when training students). We usually cleaned mounted and covered slides in methylated spirits with an old toothbrush and a single edge razor blade. Not the sort of thing to do casually with old optical glass!

Xylene is nasty stuff. It will help remove epoxy resin, though.

[Steven Tribe]

Thanks Graham! I played with a needle too - to drag the bubbles to the surface or to the edge of the clump. The problem was that there was always one that I didn't spot. You only have about a minute before the two faces to be joined start to cool down to a temperature making the join difficult. I don't think the curing time is very critical - I haven't noticed any discolouration - even after 4 hours cooking.

[Steven Tribe]

HEATING THE LENSES,JOINING AND FIXING THE TWO LENSES.

Originally the two component lenses were warmed up and baked on an iron worktable with a gas burner underneath. I recommend use of the kitchen oven - with the folowing stages:

- warm lenses up in the oven (ten minutes).
- remove the lenses and check surfaces.
- apply balsam and join the lenses.
- check depth, approximate allignment and absence of air bubbles/foreign objects.
- tie the lens together with dental floss.
- replace in oven and bake at 50-100 deg.
- remove and reassess allignment.


The second and third steps have to be done before the lens sufaces cool down too much (less than about 50 degrees?). This is especialy true of the bi-convex flint which has only about 25% of the mass of the crown concave/convex. So it absolutely necessary to have all materials ready at the work place. In particular, and open container of balsam, lots of loose paper towels to act as an insulating device and for removing excess balsam from fingers. In addition a few sheets of optical cleaning paper and a cut length of about 50cm of dental floss.

Photo 1 shows the layout for working tray which is put into and extracted from the oven. The metal tray will help keep a stable temperature. The newspaper is to protect from soiling the tray and impact damage if you are unlucky in your handling. The concave is placed flat (check this is exactly horizontal in the tray - both in the oven and the "workplace"). The flint biconvex is placed with the joining surface up and with a cushion of paper underneath so the hot edges can grasped without a struggle.

So now it is easy. Place the tray in the hot oven - wait 10 minutes for everything to warm up. Remove the tray. Check for foreign objects on the two surfaces and wipe off. These surfaces appear to remain clean in the oven environment.
Then apply/melt down a blob of balsam as show in the earlier section as near the middle as possible. Size? about 2/3 pea size. Be prepared for a violent (but non-hazardous) smell. Lift the biconvex by the edge, reverse it and place carefully down in the right place. Holding it completely parallel to the lens with the balsam seems to work best. The gravity will enough to force the balsam up to edge (and beyond). Do not worry about alignment at this stage. Before the outside surfaces get covered with surplus balsam, check for the absence of air bubbles/foreign objects. If you must take it up remember it is still warm and the flint really floats about so keep it horizontal.

Once the cementing has been judge OK you can regulate the allignment. Before the cement begins to set you have to ensure that the two lenses are as close together as possible. Old timers with their gas heated tables used a cork for this. A couple of thumbs placed both sides of the centre with gentle pressure should achieve this. Then the 3 dimensional alignment has to checked. This can be difficult as the similar indexs makes optical reference point hard to find. Fortunately, lens makers designed their cementing surfaces to facilitate accurate positioning.

As the lens assembly cools and the cement thickens it becomes possible it wrap the lens in dental floss. This material looks like it was made for this very purpose. It doesn't slip of the round corners. cuts into the excess, hardening, balsam and increased tension in the later "baking". Photo 2 shows the captive lens.

When you are satisfied, the tray is replaced in the oven (remember to keep it horizontal) for an hour or so at between 60 and 100.

Next time it will be cleaning and optical checks of the alignment.

[Steven Tribe]

FINAL STAGE: CLEANING, REMOUNTING IN LENS CELL AND CHECKING ALIGNMENT


The tray is allowed to cool down. The assembly will look very messy - with surplus solidified balsam, stuck shreads of paper and the floss threads. Cut the threads through on the ground glass side. Pull off carefully. I was always been sick of the smell of xylene by this stage and have user lesser potent solvents to scrape and rub off the surplus balsam. The mechanical activity is unavoidable unless the original dosage of balsam was exactly right. I left some balsam on the side edges to provide a cushion for the fit in the brass cell. The brass edging on the cell was pushed down with a hardwood edge. The brass edge tends to "bounce back" so this has to be repeated a few times until the lens cannot turn in the mount or rattle. Some dulling black enamel will have fallen off so a touch up with a paint brush will be necessary and may even help the physical seal.

The next section, I think anyway, is correct so I would grateful if someone could quickly step in if I have overlooked/misunderstood something.

If you have two symmetrical cells - and only one has been redone - then you can use that as a benchmark for the "new" cell. This has the rather tedious consequence that if the "old" cell turns out to be faulty - you have a new rebalsaming job in front of you! This is not just a theoretical problem - lenses can and do "slip" in relation to each other without there being any sign of balsam deteriorations!

The first test is the seen reflections from a pencil of light from a torch (or low power laser?). In this case, the purpose is not to identify how the doublet is built up but to confirm that all the reflections can be made to stand in a straight line "hidding behind each" by altering the angle of the lens. You could check the "old" lens too at the same time.

If you get past this test then there is a more demanding test. Mount the old lens alone the barrel - about halfway in, with no play in the threads - but still with ease of rotation. Mount the objective on any camera with an open back and set-up for and measurement of focal length on an interior pale wall for a bright clearly defined small bright object (sun/lamp). The use of the open back/wall rather than ground glass is because the focal length gets pretty big for single cells. Lock down the camera and tripod and check that the front and rear (the wall, in this case) are exactly parallel. Make a pencil mark aroung the focussed bright spot, which should be well away from the centre of the image. Ask permission from the head of the household first. Rotate the barrel in the mounting flange and see if the position changes through the 360 degree turn. Repeat the experiment with the "new" lens. Movement away from the original position during the turn is not a good sign - especialy if there is difference between the old and new lens. Use the other end of the barrel if there is difference in thread sizes for the two cells. This could also be caused by imperfect set-up or that the threads/mounting are not as they should be. I don't think there is any aberation can cause this "wandering" image through a 360 degree turn. Please let me know if there is.

Do not despair if things havn't worked out to well! It may be possible to make adjustments if the cement isn't to hard. The internal cement will still be comparatively soft. The ancient method was to true up the lens on a lathe at this stage.

I'll come back again ( unless told not too! ) with some additional illustrations of two other kinds of cell mounts:

[Steven Tribe]

For the record - here are photos of the completed cell, comparison with the original rear cell and the Suter objective. As good as new perhaps - certainly worth the £25 investment in buying the aplanat originally.

[rguinter]

I am not sure how easily methylene chloride (CH2Cl2) is available anymore. It used to be the active component in really effective paint removers. Perhaps "wicked" was an understatement. The commericial product was rather gel like so there was time enough to place a dollop in a glass container (not plastic here) close the lid and retreat quickly inside.

Must still be available someplace. My facility still has several mid-size storage tanks holding it. My first experience with it was in early 1970s when I worked as a clinical manufacturing technician in the pharmaceutical business. It was the solvent of choice for film-coating pharmaceutical tablets. Wicked is indeed not the word to describe a work environment with many hundreds, perhaps thousands of ppm methylene chloride vapor in the breathing zone. I can say from experience that one runs in, holds their breath as long as possible, makes adjustments, and runs back out of the room. And the vapor will make every sweating pore in your body itch like you've been dipped in acid.

Very pleasant stuff... but a surprisingly agreeable odor in very low concentration.

Regards. Bob G.

[Jack Dahlgren]

Great set of posts! I always enjoy reading about how to repair things. It is good to hear about what went wrong as well.

[suzyj]

Steven, you're wonderful!

Thankyou so much for this. I've been struggling to recement an eyepiece doublet.

My first try (after cleaning all the old cement off with acetone) was to pop the elements in a frying pan on low heat on the stovetop, and put a little bit of Canada balsam on the concave surface to melt (my balsam came as solid chunks).

Unfortunately I was unable to get the bubbles out. I had a go at leaving it on the stovetop to cook the bubbles out, but the balsam overheated and went yellow.

So then I tried dissolving a chunk of balsam in acetone, and putting a drop in the middle, then putting the other lens on top. This was much the same - still bubbles and voids.

Finally, thanks to your writeup, I tried preheating the elements in the oven to around 80 degrees, then putting a drop of my dissolved balsam on the concave element. This time the balsam flowed really nicely. It's in the oven at the moment baking for an hour at 80 degrees, but so far it looks like there are no bubbles :)

Again, thanks a million for the writeup.

[John Schneider]

Must still be available someplace. My facility still has several mid-size storage tanks holding it. My first experience with it was in early 1970s when I worked as a clinical manufacturing technician in the pharmaceutical business.

Regards. Bob G.

In the past methylene chloride was used as a solvent to remove caffeine from coffee; supposedly the residual solvent was low enough to render the decaffeinated coffee safe to drink (not for me, however).

This is a great thread. What do you think about asking for a new Forum that would cover more technical matters like camera and bellows construction, lens recementing, shutter CLA, etc.?

[Steven Tribe]

I proposed a new section last December!

-to include project descriptions with place for others experience.
-to include gift of materials ( I will have a lot of small pieces of cuban mahogany to dispose of later this year) for repair.

I think bellows construction is quite well covered already. I personally think that only a few shutter designs are suitable for the average person to meddle with!

I am starting on a method for the production of Waterhouse stops suitable for easily available tools which I will post sometime soon. I will add some material in this thread very soon with experience with other achromates. It seems that about 7 days xylene soaking for separation applies to just about all large lenses ( 50mm).

[JimL]

I am not sure how easily methylene chloride (CH2Cl2) is available anymore. It used to be the active component in really effective paint removers. Perhaps "wicked" was an understatement. The commericial product was rather gel like so there was time enough to place a dollop in a glass container (not plastic here) close the lid and retreat quickly inside.

Methylene chloride is readily available at plastics suppliers, as it's used as a solvent for joining plastic materials such as styrene and acrylic.

[Steven Tribe]

This is a update.
I have done three more balsam jobs since the last posting.
A few more tips - based on these extra experiences.

Temperature/Times:
The prewarming of the lenses before applying a drop of balsam works well at around 60 degrees C - there is no need to heat it up for long.

I have found that "baking" at around 75 degress C is enough to stiffen the balsam after assembly. An hour is sufficient.

I have found that using acetone for removing excess balsam and finger marks is the best solvent on a piece of absorbent papir. The solvent remains in the paper and will not seep down to the balsam layer.

Do not bake too long with excess balsam on the lens. I forgot a lens pair for 3 hours and the excess balsam formed a layer which was no longer soluble in organic solvents.

I enclose a before and after shot of a landscape meniscus. Received to-day and repaired to-day ( a very wet day outside - like October) ! This was a "quicky" as the lens had a screw retaining mount and the separation of the two halves was already complete.

[SAShruby]

Canada Balsam Source I (http://naturalpigments.com/detail.asp?PRODUCT_ID=510-33CAN04)

Canada Balsam Source II (http://store.studioproducts.com/)

Canada Balsam Source III (http://www.merck-chemicals.com/canada-balsam/MDA_CHEM-101691/p_6Jyb.s1LbawAAAEWZeEfVhTl)

[c.d.ewen]

Canada Balsam Source IV (http://www.postapplescientific.com/)

Can't link directly; you must search for "Canada Balsam"

Charley

[CP Goerz]

A hearty pat on the back for the posts Steve, I've had a bottle of balsam in my drawer for ages...maybe I'll use it now :-)

[Steven Tribe]

Thanks Andrew!
None of the purchases from you needed any treatment though. The good thing about balsam is that one has more time for checking allignment, a mistake can be easily rectified and excess balsam on the edge provides an excellent "fitting" medium in the brass mount.

[Sethasaurus]

Thanks for sharing your experience, Steven.
I have a lens I want to re-cement and I found this info which will also be useful to people:
http://www.skgrimes.com/popsci/index.htm
http://www.skgrimes.com/popsci/pops/index.htm
http://www.skgrimes.com/popsci/burnish/index.htm

[Steven Tribe]

I think some of these Grimes' notes are new.
Unfortunately, we don't all have a large lathe in the garage! The only problems I have with his description are
- heating as a means of separation. I have seen many cases of completely dried out balsam that wouldn't soften.
- heating lens + balsam in place. Balsam develops a "skin" on the top surface very quickly which will prevent satisfactory adhesion to the "top" lens. I think separately heated lenses, addition of balsam, placing the top lens on top quickly, obtaining the right fit, binding together, followed by gentle heating, is the best method.

I have removed the burnishing holding the lens with an ordinary file. It requires discipline and I always protect the glass surface with tape. It is not necessary to file through the complete thickness before it can be "broken off".

[desertrat]

Kremer Pigmente in Germany sells canada balsam:

http://kremer-pigmente.de/shopint/index.php?cat=0211&lang=ENG&product=62110

They also sell all kinds of pigments, resins, varnishes, adhesives, just about anything an artist or musical instrument maker might want. Some of the other resins might be good for making things like retouching varnish from old recipes.

In the US, Wood Finishing Enterprises sells similar items:

http://www.woodfinishingenterprises.com/varnish.html

I haven't bought anything from either of these companies, but might for future projects.

That's a great article on recementing lenses. I have one that needs to be done.

[Steven Tribe]

Interesting products! And in Euroland too.

I am rapidly coming to the conclusion that as many as 1/2 of our 19th C objectives could do with a renewal of the canada balsam. When I compare the redone cells with an original cell (which seemed OK), there is a very marked difference in the general clarity of the two! Even those without discoloured edges or crystalline "flakes".

[desertrat]

I like the idea of using balsam to recement old lenses. Modern adhesives have certain advantages, but the big advantage of balsam is that it can be done over again if it doesn't turn out right the first time. I need a process that's reversible, because very likely I won't get it right the first time.

[Steven Tribe]

Just an update!

My first bottle of Canada Balsam no longer pours, but is still usable by geting a piece on the end of a glass rod, or similar, and letting it contact melt off onto the warm glass.

This time I have done an older lens - the Ross Actinic doublet - the Ordinary Angle version. This is one of the attempts in the battle for the "RR" design!

About half the balsam layer was discolored yellow. It took the usual 7 days of Xylol soaking. Once again, the balsam had left a Chalk looking deposit over the whole of the concave surface. Again this was removable quite easily with water based solvents.

This was very different type of lens mounting. The photo shows the cell with half the blacking enamel in place. The cemented lens is much smaller than the mounted lens - which is part covered with black paint or shows its mat rear surface.
This is good in respect of escaping the trouble with fiddling with the brass but means that fixing the cleaning lens in the balsam hardening process is more tricky. It also means that a total balsam failure would mean the demise of the lens as it would fall off.
I have just painted one side of the lens to show the GG surface of the fixed lens. The other side is fully polished. I suppose this use of "oversized" lenses is the price you have to pay for standardisation of mounts/barrels. This is the 4x5" size.

[GSX4]

Are there companies out there that will do a re-cement for a fee??? I have a darlot with a seperation in the front element, while not overly bad for wet plate type work, I would like to make it 100% again. More importantly, seperating and recementing the lenses so that the original Darlot pencil marking on the edge is not disturbed would be ideal.... Any ideas?

[Steven Tribe]

I think the original Darlot marks would be untouched by traditional Canada Balsam. I'll do some experiments with pencil marks next time I split an achromat.
In the soaking/delamination you can get them to restrict the amount of fluid in the container so it only reaches the line of cement. Or/And you could use a water-based clear varnish on the sides and let it dry out before the separation.
I believe the traditional Grimes organisation does (sub-contracts?) balsam work.
I hear that the UK contact for Balsam, Balham Optics, has ceased to exist. Perhaps they will re-emerge as the Bellows company in Birmingham did with a employee buy out.

[Steven Tribe]

I have just "forged" the usual Darlot pencil marks on the side of an achromat. It is not removed by flowing xylol and required quite a lot of rubbing with a xylol soaked cloth to remove all traces. Liquid Canada Balsam did not disturb or lift the pencil marks.

[GSX4]

Thanks Steven

[Steven Tribe]

This is an update - mostly because some people have sent PMs recently about feasibility of doing it themselves.

1. Aging of Canada Balsam in small bottles.

I have 2 small bottles bought in 2009.
I have used about half of 1 bottle and have just started the 2nd bottle yesterday. The 3 year balsam in the full bottle is still almost without colour but the 1/2 full bottle does now have a noticable yellow tint. This, I suppose, is the result of oxidation. I think it is perfectly useable however.

2. Preheating and baking.

I now limit the prewarming to around 65 grad C. I also preheat the glass rod used to "fish-up" balsam from the container. I restrict the "baking" to a couple of hours at the same temperature (65C).

3. Applying the balsam to the concave surface.

I use a glass rod to apply the balsam at the centre of the concave lens. Reason - attempts at pouring, both mess up the balsam glass seal and (can) create tiny air bubbles which are a problem.

4. Even clear separation can have insoluble deposits on surfaces. Remove with finger nail.

5. Expect the solvent to loosen the edge black paint!

6. Don't expect the two (or more pieces) to fall away from each other. When I can see the liquid phase has nearly reached the centre, I dry the lens and push across. If there is some displacement, I begin to rotate carefully. Repeat soak if no success!

Could a Moderator move this to the DIY section?

Will be trying with a 4 glass lens in the next week (Zeiss Protar series VIIa).

[twalsh341]

I am not sure how easily methylene chloride (CH2Cl2) is available anymore. It used to be the active component in really effective paint removers. Perhaps "wicked" was an understatement. The commericial product was rather gel like so there was time enough to place a dollop in a glass container (not plastic here) close the lid and retreat quickly inside.

Methylene chloride is the Weld-On #3 solvent for use in sticking acrylic together. Readily available hobby item.

[rdenney]

Rick "moved at the request of the OP" Denney

[Jim C.]

Methylene chloride is the Weld-On #3 solvent for use in sticking acrylic together. Readily available hobby item.

Pure methylene chloride seems to be unavailable at the retail level, chem supply places might have it,
the Weld-On #3 has an added components to it, I have a bottle of Methylene Chloride from yore that I recently
came across and the odor doesn't have a pungency to it that Weld On has.
You don't want to damage the glass !

[patrickjames]

I have had luck separating elements with Acetone. I recemented a couple of Computar DL enlarging lenses a couple of years ago. They probably had some modern type of cement, but they are prone to separation. The Acetone worked in about a day turning the cement cloudy. I recemented them with Balsam in the oven with small machinist's steel V-blocks. Afterwards I used a Sakura pigment brush/pen to darken the edges which worked quite well. I am pretty sure I used this thread as reference, so thanks Steven.

[Steven Tribe]

Acetone is a very good solvent.
But it is something of a problem child outside of a laboratory.
It boils at about 56 deg C, Has a flashpoint of minus 15 deg C (can cause explosions above -15 C even when mixed with water!).
Xylol (xylene) boils at 140 deg C and has a flashpoint of plus 56 deg C.
Methylene chorlide (dichor-methane) boils at around 40 deg C but is not inflammable alone - it burns at around 600 deg C.

The vapour pressure of Xylol (amount of xylol in the air above a vessel) will aways be less than acetone.

All are nasty solvents - healthwise - short and long term.

[Steven Tribe]

Dear moderators!

Someone has just asked me what has happened to the photos which I have uploaded in this thread. The whole thread seems rather less than useful in its present state!

[Fr. Mark]

Interesting thread. Methylene chloride will go right through most reasonable lab gloves like what some of us use for developing film. i.e. medical exam gloves. Even two layers of latex gloves are no help. I've tried. I used to DCM by the multiple gallons when I was a researcher in the pharmaceutical world. nitrile gloves are better but the thickness of the gloves required to truly exclude DCM mades handling delicate lenses troublesome. I would second the thought that acetone is a wonderful solvent, but it is very flammable/explosive and finds pilot lights..., it is less toxic (possibly) than benzene, toluene, xylene and methylene chloride/dichlormethane (synonyms). I think we would all be wise to limit chemical exposure to photographic chemicals and solvents etc. but also not be too phobic about it. Lots of chemists used to work without gloves, without fume hoods, and wash their hands in 1:1 acetone:benzene and lived to ripe old ages. Sure, there's a subset that died young, but most of those stories I've been able to track down involved far more toxic molecules than common or uncommon solvents. Also, the formation of formaldehyde from DCM? I'm skeptical your body has the biochemistry to remove the first chlorine atom. Sure, I can do it in the lab, but the body, I don't know. Also, your body can and does make acetone in some situations (high protein, low carb diets for instance). Again, I'm not suggesting we be too cavalier with these materials, but also, let's not be so phobic either. The universe is made of chemicals, a skiff of electromagnetic energy, plasma, and a lot of vacuum. About picking solvents for tasks: in general molecules of larger size are dissolved by molecules of smaller size with similar chemical characteristics. Ex. Sugar molecules have a "coating" of what are arguably 2/3 of a water molecule. Sugar dissolves well in water. Table Salt is ionic and water has strong (for a covalent molecule) charge separation and dissolves table salt. Candle wax is mostly hydrocarbon and kerosene, a sorter length hydrocarbon, is pretty good for getting candle wax off of surfaces in church. And kerosene can be gotten rid of with isopropanol and or some soaps which won't touch candle wax. I think Canada Balsam is a resin from a coniferous tree, probably distilled/waste from making turpentine. So, it's a hydrocarbon or a lightly modified one (maybe some oxygen atoms?). It's not surprising that hydrocarbons, like toluene and xylene act as solvents for it. Gasoline and kerosene and diesel and Coleman fuel might also work but are much more flammable and the peculiar nature of benzene/toluene/xylene of having an "aromatic" ring in them may also help in getting the Balsam dissolved. DCM is a chlorinated hydrocarbon. It has a smidgen more polarity than true hydrocarbons and a certain amount of "squishiness" of electron density due to the 2 chlorines that mimic, in a way, the aromatic ring in Xylene's "squishiness" that also make it make sense for getting Balsam apart. I'm suspicious that Canada balsam may have a little solvent in it to start with and if it gets too "stiff" adding a tiny amount of very pure solvent back may restore it to workability. On the other hand, it might be cured by polymerization like the oils in oil paints but that would tend to preclude getting it apart with solvents. Once molecules get to a certain size (in general) you can't solubilize them i.e. starch is a polymer of sugar and isn't soluble in water.

[Michael Clark]

The pictures would have very useful.
Dear moderators!

Someone has just asked me what has happened to the photos which I have uploaded in this thread. The whole thread seems rather less than useful in its present state!

[Jim Galli]

I do hope the pics return. Would like to re-read.

[Michael Clark]

I'm thinking that they (pictures) must have, were originally posted on a different site and have expired on that different site, like a lot of the photo's here and on other web sites, too bad.!!

[Steven Tribe]

No. They were uploaded to LFPF.

[Michael Clark]

Well lets hope the mods will be able to retrieve them.

[rrunnertexas]

163791

[rrunnertexas]

The picture above is a shot of the lens as removed from my 1890 model Blair 4x5 detective camera. The lens is suffering from severe balsam separation. I decided to try and make the repair myself, inspired by this thread. Since the original thread is older, it seems the photos have disappeared. So, during the process of restoration, I am posting a few new pictures just in case this is helpful in the future to another faced with the same lens problem.

163792

Slowly bringing the lens up to temperature in a pan of water.

[rrunnertexas]

163793

After about 10 minutes of warming, (ok, it's hot now) the original 125+ year old balsam is melting and the 2 pieces came apart.

[rrunnertexas]

163794

After cooling in the pan to room temperature, I removed the lenses and put them on a paper towel to dry.

Next step is to wipe the lenses clean with alcohol.

More to follow.

[rrunnertexas]

163894

After cleaning both lenses with alcohol, I placed a small piece of blue tape on each of the "facing out" sides of the lens. Then cleaned again with a mild window cleaner to make sure all the old balsam was gone.

[rrunnertexas]

163895

Pressing both lens elements together caused the balsam to spread out to the edges of the lens. After double checking the alignment, I used a simple Craftsman brand pressure clamp to hold the lenses together as the balsam dries.

[rrunnertexas]

More to follow when dry.

Oh, and a huge thank you to Steven for his inspiration.

[Steven Tribe]

Based on old and recent experience, I have found that the occasional devitrification which occurs seems to be associated with:-

Crown glass used in both Petzval achromats and Rapid Rectilinear (Aplanat) doublets. This is a glass which was used extensively from the start of Photography.

It is a phenomenum which starts at the surface and can spread into the body of the lens. Both degrees of attack mean a scrap lens. The flint glass is always OK,

For sometime I thought that use of aqueous solutions used in the separation of cemented lenses might be the cause (microscopic defusion of water molecules into the glass skin) but this is not so. All glass failures have occured during gentle warming. I used to recommend heating as a way of speeding up the slow solvent dissolution of hardened balsam. I now think that the only safe way to harden the new balsam is warming to just over room temperatures in one process. I have examples of repeated warming to just under 100 degree which went OK the first few times, then, suddenly it happened in just a few minutes! Repeated temperature stress is a killer for crown glass.

[Mark Sawyer]

Resurrecting a year-and-a-half-old thread as it seems the best reference article about re-cementing with Canadian Balsam on the forum, (thanks, Steven!).

I just ordered some Balsam from Surplus Shed, and have been reading about using it from many sources around the net. (I'm experienced with UV-cure, but would rather go with Canadian Balsam because it's cheaper, more reversible, and has a very long shelf life (UV cement is only good for 4 months). I also found an old reference that UV cements have a different refractive index and spectral transmission than Canadian Balsam, but I doubt that has any significant effect.

I did find one source that disagreed with the drying-under-heat technique referenced throughout this thread and wanted some feedback on it. From http://forum.mflenses.com/re-cementing-doublet-elements-with-canadian-balsam-t34467.html

"Leave your doublet undisturbed in a quiet and warm place for a minimum of 1 week and maybe as long as 1 month. A sunny window is good, but do not let your doublet reach a temperature of higher than about 90 degrees F or the solvent in the solution will bubble (a disaster for you as bubbles were probably the problem you were repairing in the first place) Balsam around the edge will dry rather quickly, however the balsam in the very center will take possibly years to dry...and it is possible that it may never dry completely I suppose."

Any thoughts on drying/curing Canadian Balsam?

[Steven Tribe]

"Drying under heat"
A belated answer!
I have progressively reduced the maximum temperature for setting the edge balsam after reassembly! I suppose that room temperature would be good enough if can wait an extra few days.
I regard all the suggestions of "self healing" through warming the lens without disolving the dude balsam as dangerous heresy!
Would like to underline that the use of 6 or more rubber bands across the lens, like hour marks on a clockface, is the best way to allow fine adjustments with slippage. I still recommend xylol rather than the more dangerous, acetone!