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strained glass

ATM beginner
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#1 Astro Daddy

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Posted 22 April 2018 - 03:51 PM

Greeting all
I was finally able to see the strain in my practice glass. I tried every pair of sunglasses I had laying around none were polarized of course. I purchased a cheap pair from the dollar store to see if they would work. I knew this glass had strain because I was told that on the classified page. I place the glass in front of my computer screen and ran paint with a white screen put my new glasses on and with anticipation saw very faint shadows. I was confused and started to figure the glasses were not that polarized,  it's suppose to have some pretty good strain. Then for some reason when I started taking them off I seen it. For some reason I had to turn the glasses about 45 deg. to see it.

DSCF0007.JPG


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#2 Richard O'Neill

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Posted 22 April 2018 - 04:30 PM

You can see the same effect on outdoor scenes when looking through polarized sunglasses if you rotate them. Polarization effects abound in reflected sunlight. Bees use skylight polarization to navigate. We can do the same with simple technology, even on an overcast day.

 

http://www.skyandtel...-to-egg-nebula/

 

Also see Sky & Telescope May, 1997 'Vikings and Polarization Sundials'. An easy DIY project.


Edited by Richard O'Neill, 22 April 2018 - 04:39 PM.

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#3 Astro Daddy

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Posted 22 April 2018 - 05:46 PM

Thanks for the link Richard

I thought maybe the sunglass lens were made wrong or something. 

John



#4 mark cowan

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Posted 22 April 2018 - 07:12 PM

Yup, that would be only glass for practice, then.



#5 Pinbout

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Posted 22 April 2018 - 08:15 PM

Yup, that would be only glass for practice, then.

Tool



#6 Astro Daddy

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Posted 22 April 2018 - 08:25 PM

Yes that was the goal and most likely will become a tool. I just hope the mirror from my Zhumell doesn't look like that. Should you strip the finish from a coated mirror of could you just go ahead and polish it off?

John



#7 Pinbout

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Posted 22 April 2018 - 08:28 PM

Yes that was the goal and most likely will become a tool. I just hope the mirror from my Zhumell doesn't look like that. Should you strip the finish from a coated mirror of could you just go ahead and polish it off?

John

Did you test the mirror 1st? 

 

Id use ferric chloride to strip it, polishing the coatings off could sleek the glasss...sssss


Edited by Pinbout, 22 April 2018 - 08:28 PM.


#8 Astro Daddy

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Posted 22 April 2018 - 08:40 PM

Yes this is the mirror that you said the figure didn't look that bad on. But when you do a Foucault test it has line radiating from the center not smooth like I see on examples of good mirrors. Also I could never use my 4.7mmm eyepiece, with the used ES mirror I have in it now I have been able to use it a lot. But even the ES mirror seems to have a turned edge according to star test examples, but even with that I can resolve doubles the Zhumell never could.

John



#9 Astro Daddy

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Posted 22 April 2018 - 08:53 PM

Did you test the mirror 1st? 

 

Id use ferric chloride to strip it, polishing the coatings off could sleek the glasss...sssss

Would a liter be enough for the job?



#10 Mike Lockwood

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Posted 22 April 2018 - 09:32 PM

Did you test the mirror 1st?

Id use ferric chloride to strip it, polishing the coatings off could sleek the glasss...sssss

I've never seen that happen and have done it many times.  The stuff you are polishing off is the same hardness as the glass or softer.  It's fun and very educational to watch weird things appear as you polish away the coating.

 

Would a liter be enough for the job?

Way too much.  Saturate a piece of tissue paper or thin paper towel that is on the surface of the mirror.  Should take a few tablespoons.


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#11 Oregon-raybender

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Posted 23 April 2018 - 12:43 AM

I like to ask a simple question. I always used "Green River" to strip AL and silver coatings, place some on a tissue and the coating always comes off and for me safer to use! It was John Strong's choice.

 

Why are folks rushing off to use Ferric Chloride? confused1.gif

 

Starry Nights. waytogo.gif



#12 mark cowan

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Posted 23 April 2018 - 04:49 AM

Ferric chloride works really well, I've been using the same bottle from Radio Shack for well over a decade.  You pour it on, let it soak, and pour it off and back into the bottle.  Overcoats may require more time but there are always a few pinholes to let it in.  Here used under plastic with newspapers to spread it out:

 

stripping coating with ferric chloride.jpg


Edited by mark cowan, 23 April 2018 - 04:52 AM.

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#13 ccaissie

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Posted 23 April 2018 - 07:29 AM

Well, your polarization method is certainly more exacting than my quick test.  You revealed way more strain than I expected.  

 

Have fun polishing!  Getting out those initial machine-made zones will be instructive, and the TDE will be fun to work with.  

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Edited by ccaissie, 23 April 2018 - 07:30 AM.

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#14 Ed Jones

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Posted 23 April 2018 - 08:03 AM

What is "Green River"?  Is it caustic?  If so I woudn't use it.



#15 Astro Daddy

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Posted 23 April 2018 - 08:54 AM

Well, your polarization method is certainly more exacting than my quick test.  You revealed way more strain than I expected.  

 

Have fun polishing!  Getting out those initial machine-made zones will be instructive, and the TDE will be fun to work with.  

Yep I am getting the needed things together now. I just went ahead and purchased a 10" grinding kit from first hand discovery . It has the grits, pitch and polish. Still need to build my Diy spherometer. I want to change blank.from it's f6 sag to f8. That is if I can find enough room to setup a Foucault test. I just didn't realize how much difference that made until i stretched out the tape measure.

John



#16 Steve Dodds

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Posted 23 April 2018 - 09:54 AM

Ferric Chloride has no fumes so It's safe to use inside.  It only eats metal so if you get it on you it's no big deal.


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#17 Mike Lockwood

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Posted 23 April 2018 - 09:55 AM

What is "Green River"?  Is it caustic?  If so I woudn't use it.

No, it is acidic.
 
Here's a quote from this article:  https://www.pfonline...s/mirror-mirror
 
“Green river is a name that someone came up with many years ago for the solution we use to strip the old aluminum coating,” Baker says. “The basic formula for green river is two quarts of distilled water, one quart hydrochloric acid and one ounce of cupric sulfate.
 

Ferric Chloride has no fumes so It's safe to use inside. It only eats metal so if you get it on you it's no big deal.

I think there are some fumes, I have seen it corrode nearby metal.  So I try to use it away from electronics or other things that I care about.


Edited by Mike Lockwood, 23 April 2018 - 10:05 AM.


#18 Pinbout

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Posted 23 April 2018 - 11:44 AM

Ferric Chloride has no fumes so It's safe to use inside.  It only eats metal so if you get it on you it's no big deal.

I keep it in a freezer bag... if the mirror is small enough...it does smell when I open the bag.

 

post-106859-0-20227300-1523125838_thumb.


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#19 Oregon-raybender

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Posted 23 April 2018 - 12:27 PM

I know this went off topic.

 

Sorry, I should have explained what "Green River" was. We used it at Tinsley to remove the silver coating we sprayed on the optics for test. I never had an issue with the fumes from it, that is why we used it. We kept it in a squeeze bottle and used it as needed. The mixture came from John Strong of Cal Tech, the person who discovered the method of coating AL. The mixture is used at Lick, Mt Palomar, LLNL and perhaps others as well bow.gif

 

There are YouTube videos on the 200 inch. Telescope Making #46 has an articles on AL coating and re-coating the 200 inch where Green River is mention.  imawake.gif

 

At Tinsley we would cover the optic with tissue and pour a small amount on it, less than a 1/2 cup (6 inch mirror). This reduces the amount and any issues with heavy fumes. Our mixture was made in a smaller amount, about a liter and far less acid than stated. We mixed the cupric sulfate and water first then added (muriatic, for pools) acid until it turned green, thus the name.

 

I just checked to see if there is something new. I found that Walmart sells "Klean Strip Green Muriatic Acid" with a 90% reduction of fumes. It appears to be a reduction of the percentage of acid, with green color? added says their MSDS / SDS.

 

Safety First: Always read, understand and follow the requirements of any chemical you use, get the MSDS or SDS on the product first, most if not all are available on line. Use all precautions and safety equipment, protect yourself. goodjob.gif

 

This may be a subject for members of CN who are chemists (who know better than us) and have their input (perhaps run some tests and report) on which to use, perhaps both are just work fine. graduate.sml.gif

 

Starry Nights waytogo.gif



#20 Astro Daddy

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Posted 23 April 2018 - 01:36 PM

I know this went off topic.

 

Sorry, I should have explained what "Green River" was. We used it at Tinsley to remove the silver coating we sprayed on the optics for test. I never had an issue with the fumes from it, that is why we used it. We kept it in a squeeze bottle and used it as needed. The mixture came from John Strong of Cal Tech, the person who discovered the method of coating AL. The mixture is used at Lick, Mt Palomar, LLNL and perhaps others as well bow.gif

 

There are YouTube videos on the 200 inch. Telescope Making #46 has an articles on AL coating and re-coating the 200 inch where Green River is mention.  imawake.gif

 

At Tinsley we would cover the optic with tissue and pour a small amount on it, less than a 1/2 cup (6 inch mirror). This reduces the amount and any issues with heavy fumes. Our mixture was made in a smaller amount, about a liter and far less acid than stated. We mixed the cupric sulfate and water first then added (muriatic, for pools) acid until it turned green, thus the name.

 

I just checked to see if there is something new. I found that Walmart sells "Klean Strip Green Muriatic Acid" with a 90% reduction of fumes. It appears to be a reduction of the percentage of acid, with green color? added says their MSDS / SDS.

 

Safety First: Always read, understand and follow the requirements of any chemical you use, get the MSDS or SDS on the product first, most if not all are available on line. Use all precautions and safety equipment, protect yourself. goodjob.gif

 

This may be a subject for members of CN who are chemists (who know better than us) and have their input (perhaps run some tests and report) on which to use, perhaps both are just work fine. graduate.sml.gif

 

Starry Nights waytogo.gif

Not off topic at all. I need to remove the coating on my next mirror and check for stress. I am always learning new things here. But to be honest if there is a product which does the job and does not require mixing several  chemicals together then I think I  prefer to keep it simple with just the one product smile.gif

John



#21 Pinbout

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Posted 23 April 2018 - 01:42 PM

Not off topic at all. I need to remove the coating on my next mirror and check for stress. I am always learning new things here. But to be honest if there is a product which does the job and does not require mixing several  chemicals together then I think I  prefer to keep it simple with just the one product smile.gif

John

as if the mirror is big I do it out side...

 

https://youtu.be/e-W...CtC5BfqQcW8rBwA


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#22 Astro Daddy

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Posted 06 May 2018 - 07:35 PM

Hello again

I was finally able to strip the coating off of my Zhumell mirror. I am disappointed as this one is stressed too. But is it too much?

DSCF0016.JPG

John



#23 Pinbout

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Posted 06 May 2018 - 08:24 PM

its no fun to figure, no wonder high powers sucked. did you ever do a ronchi test going thru focus?


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#24 Astro Daddy

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Posted 06 May 2018 - 08:40 PM

I mostly was practicing the Foucault test with it. But I did attempt some photos using the poncho screen 133lpi.

Z10  1 (2 18 2018 4 53 PM)
 
Z10  1 (2 18 2018 4 51 PM)
I was searching for images like mine on Google and found one exactly like mine from Ed Jones site. He said that is was an example of a severely stressed piece of glass.

Looks like I have 2 tools now.

John



#25 Pinbout

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Posted 06 May 2018 - 08:56 PM

its not badly figured

 

10inf5.JPG




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