How Thick is Balsam Fir Gum Supposed To Be?

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sissysphoto

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I've got a little 1 ounce glass bottle of Canadian Balsam fir gum wih a plastic screw on eyedropper type of top. I suppose it's been 5 years since I bought it and only used about a drop of it and screwed the top back o and never opened it since. The rubber part of the eyedropper is still pliable and not cracked. The bottle is quite full still.
My quest is, has this stuff thickened up or was it always very thick? I can turn the bottle and the stuff will flow, but very slowly. I'm sure there has been no crystalizing. It is still clear and wet, but it sure is mighty thick. Was it always this way?
Thank you.
 

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Search engine: google; browser: Firefox 61.0.1; O.S. : Windows 10 version 1803; search term: Canadian Balsam fir gum viscosity
3rd hit down page 1: https://www.firtreegumofthenorth.com/Library.php . In the preparation and uses pdf it states its about the same as honey in consistency. The pdf also states the solvents it can be dissolved or diluted in.
 
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sissysphoto

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Thank you. I guess it does thicken up. I never was a fan of honey, so I'm not entirely sure how thick it is. But I have heard the expression "January molassis", which may be more apt. I've got an old Nikkor 35mm 2.0 with a fogged doublet. I put the doublet in a jar of acetone today. I don't think it's going to separate it though. But I'll give it a week and if I see no results, I'll put it in methylene chloride. THAT will do it for sure. But I'm going to use this stuff, although I might try some thinning experiments in the meantime.
 

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sissysphoto

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Well this is strange. 1 day in the acetone and the little doublet came right apart. And I don't see any sign of any kind of adhesive on either of the glass surfaces. Before I put it in the acetone, I noticed a bead of some kind of glue around the perimeter of the joint and assumed it was just ooze-out from the glue or resin that joined the 2 glass surfaces. The last and only time I got a doublet apart I had to clean th glue off both lens surfaces. But it doesn't look like this onh had any glue on the surfaces. I wonder if they were just joined with a bead around the outside of the joint and nothing else. But given the construction of this Nppon Kogaku 35mm f/2, just puting a bead around that joint doesn't sound very secure.The back of the front glass is slighty convex and the front of the back glass is slightly concave, as if they were to fit together but I have no way of knowing if the curvatures were ground to match perfectly for that. Or perhaps the glue on the surfaces was so thin, it just looks like there wasn't any.
 
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sissysphoto

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No, it just popped apart. But with a magnifier I was able to find places in the jagged edges of the glue bead to piece it back together.
 
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sissysphoto

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I wonder what difference it would really make if a doublet like this was put back together turned from original position. Lenses in this day and time are ground to the jillionth of an inch in precision. I suspect nobody would ever notice one bit of difference in picture quality.

On another note, it looks like this canadian balsam has indeed thickened up. It's nearly stringy when I put a blob on a piece of paper. All I have on hand is acetone , naptha, or 99% isoptopyl. I'm not going out and spend money on xylol just for this.
 

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On another note, it looks like this canadian balsam has indeed thickened up. It's nearly stringy when I put a blob on a piece of paper. All I have on hand is acetone , naptha, or 99% isoptopyl. I'm not going out and spend money on xylol just for this.
turpentine is inexpensive, use it to thin the balsam.

I wonder what difference it would really make if a doublet like this was put back together turned from original position. Lenses in this day and time are ground to the jillionth of an inch in precision. I suspect nobody would ever notice one bit of difference in picture quality.
Color fringing or other minor errors in the image or a reduction in overall image quality.
 

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I hope you made an index line or two on the side before separating. Cemented pairs are usually optically aligned.

To my knowledge centering. means aligning the optical axis of the lenses.
What you indicate with your index mark is a rotational alignment. With lenses rotationally ground that makes no senses to me.
 
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sissysphoto

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Well, I did it. I cut the gum with a wee bit of naptha, and the consistency was about what I wanted. I didn't contaminate my whole bottle with naptha. Just a dab that I needed. This is a very small doublet. I'm sure my job wasn't labaratory perfect, but I had absolutely nothing to begin with. And my job is clear now, whereas before it was a fogged worthless mess. Finding perfect center was a bit hard, but I feel sure I found it. Now to just let the job sit and dry. The lens was a free tagalong with an ELW I picked up. I had already reworked the ELW and I'm waiting on a new gear for the motor.. The ELW had some dents and dings, but I got the sheet metal straightened out pretty nicely, without paint. I discovered that the old parts prism from an FTN worked very well in this ELW. I think I'm going to be pretty happy with this outfit.
 
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sissysphoto

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BTW, I tried to keep rotational center, although it didn't make a lot of sense to me either. It was the axial center that I worked to keep more than anything.(axial or radial, I get those mixed up). Center of lens, how about that?
 
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sissysphoto

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I got an alert of this thread. My cementing job turned out very nicely. Absolutely clear as a bell. Before it was so fogged the entire lens was worthless. Since this doublet is in the middle of the other 6 elements, I'm going to let it sit out. I could put the lens back together now and go ahead and use it. But I'd rather let it sit out. If I put it back in to finish drying, I might end up with out-gassing fogging the the adjacent elements.

As for the oil idea, I didn't care for that. For one thing, Canadian balsam is reputed to have the correct refractive index for bonding lenses. Secondly, oil would outgas. Seems to me the only good an oil repair would do is cut out newton rings.
 

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Is this the beast? https://www.mir.com.my/rb/photography/companies/nikon/nikkoresources/preAI70/35mm1.htm
35mmf2preAIopt.gif
 
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sissysphoto

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That's basically it, although you attached the ai lens. Mine is much older. But I do recognize the doublet as 3 and 4 from the front
 
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