24 in teelscope - silvering finished

自製天文望遠鏡 牛頓望遠鏡 杜蘇式 卡式 設計和磨鏡方法<br>
佛科試鏡法 佛科刀片儀 光柵試鏡法 光柵片
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註冊時間: 週四 09 10月, 2003 21:06

24 in teelscope - silvering finished

文章 Chanlunlun » 週六 12 6月, 2004 15:50

Dear ATMs,

After delaying for a few days due observation of Venus transit, the 24 inch mirror finally received its silver coating on Friday, 11th June. Originally coating process was scheduled to be carried out on Thursday, 10th June but due to technical difficulty we had to postpone the operation for one day. The silvering process is quite a story to tell.

We had spend 122 grams of silver nitrate and it was nearly all the stock we had on hand at the moment. In other words the process tolerated no failure. ( Of course we can always buy new silver nitrate, as far as we still get money supply ). We needed 3 liters of Tollen』s reagent and while preparing for it we made a serious mistake – our chem lab supplied wrong ammonia solution ( too diluted ) and the reaction did not seem to be correct – instead of making the Tollen』s reagent we made a big batch of silver oxide and mixture. Feeling that we had wasted all the silver nitrate with no hope for a second chance you could imagine how frustrated we were at that point, until someone suggested that we kept the solution overnight and started to find some concentrated ammonia solution next day. We had no idea whether the solution was stable enough for one day ( we all heard that Tollen』s reagent is very unstable, it should always be prepared freshly ) but it seemed that we had no choice.

On the next morning I tried my best to ask all chemistry teachers in school welther we had in stock very conc. ammonia solution. Thanks to their kind assistance finally in some sort of store room a dirty bottle labeling 「ammonia solution, s.g. 0.88 「 was discovered. By that time it is quite impossiible make sense about the label』s meaning but the smell seemed strong enough. Consequently all the mirror making team member gathered again at thE small "opticaL SHOP" after school trying to finish the unfinished. We poured the strong ammonia solution onto the mixture that had been lying overnight. The mixture suddenly turned clear – it did not seem all right but the procedure was being carried on anyway.( since we had no choice ) The Tollen』s reagent thus made did not seem to be correct – instead of weak tea color ( this is what the Web has said ) we got something black in color. Was it really Tollen』s reagent or something highly contaminated ? Nervously we mixed it with dextrose solution and tried it onto the mirror surface.

After two days』 effort with all its frustration and excitement, here came the most amazing moment – the mixture, having poured onto the mirror surface, turned deeply black at once. The reaction came so fast that we did not even get ready for it. With all the chaos among students shinny silver particle started floating onto the liquid surface. Within 5 minutes the solution turned light brown indicating that all reaction was completed. We quickly, absent-mindedly, nervously, chaotically poured out all the solution. A thick layer of brown mud was seen sticking onto the mirror surface....... I heard Mr. Sodium said, 「 I think we fail the process.」

Immediately the thick mud was flushed away away with a lot tape water. To our excitement a bright coating of pure white silver started to emerge. After all the mud had cleared, we actually saw a perfect coating of silver layer, so perfect that it was purely white and required no further polishing by chamois skin.

Overwhelmed with excitement we flushed the whole mirror surface with distill water and here came the second serious mistake – the bottle labeling 「distilled water」 contained no distilled water but only tape water. When the mirror dried up it was stained heavily. While the majority of stain was removed by dry polishing the silver layer with a piece of old chamois skin, stubborn spots were just left over onto the silver surface. They nevertheless did psychological harm rather than affecting truely to the performance of the mirror. The mirror looked excellent anyway.

The feeling of looking into a big silvered parabolic mirror was stunning - 98% reflectivity, at least at that moment right after burnishing, with a magnified yourself inside a huge reflecting area, it was quite a sight to see.

We have finally the whole project completely finished. All we need now is a clear night for the telescope to see its first light.

Best regards

Chan Yuk Lun
Preparation before silvering - since large volume of reagents were required we didn't use beakers but Pepsi bottles and a lot of distill water. I'd drunk a lot of Pepsi in order to collect all the bottles.
silver_prepare.jpg (54.4 KiB) 已瀏覽 9480 次
students were buzy at making the dam.
dam_making.jpg (57.5 KiB) 已瀏覽 9480 次
The finished dam to hold the liquid during silvering.
dam_finished.jpg (41.25 KiB) 已瀏覽 9480 次
最後由 Chanlunlun 於 週日 13 6月, 2004 11:57 編輯,總共編輯了 3 次。

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文章 Chanlunlun » 週六 12 6月, 2004 15:59

more photos

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註冊時間: 週四 09 10月, 2003 21:06

文章 Chanlunlun » 週六 12 6月, 2004 17:24

more photos
The finished dam was inspected. It looked good but in real situation it leaked quite seriously. Anyway it still held the solution for 5 minutes.
1_Dam_inspection.jpg (56.36 KiB) 已瀏覽 9463 次
Student was buzy at washing the mirror surface by saop solution which was followed by conc. nitric acid ( it is quite dangerous stuff, so the process was carried out by me personally )
2_soap_washing.jpg (41.87 KiB) 已瀏覽 9463 次
When silvering began, the solution turned into deep black color
3_reaction_begins.jpg (42.13 KiB) 已瀏覽 9463 次
最後由 Chanlunlun 於 週六 12 6月, 2004 17:55 編輯,總共編輯了 1 次。

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文章 Chanlunlun » 週六 12 6月, 2004 17:28

still more photos to come.........
When the reaction was close to its end the silvering solution turned into brown color.
4_nearly_finish.jpg (37.49 KiB) 已瀏覽 9462 次
When the solution was poured away, the mirror surface was covered with thick mud. It did not look good - it seemed to be a failure of the silvering process.
5_mud.jpg (36.3 KiB) 已瀏覽 9462 次
When the majority of mud was cleared the underneath white silver layer appeared. You can see the face of Mr. Sodium at bottom left.
6_washing_mud.jpg (44.12 KiB) 已瀏覽 9462 次
最後由 Chanlunlun 於 週六 12 6月, 2004 17:56 編輯,總共編輯了 1 次。

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文章 Chanlunlun » 週六 12 6月, 2004 17:46

even more photos coming ...........
The finishing of rinsing stage. Mr. Sodium helped to move the mirror to the drying table. The silver layer was brightly white.
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The rinsed mirror was undergo drying process in an upright position. You can see that the silver coating is purely white in color and is perfect in appearance, just like a fresh aluminized mirror coming out from vacuum chamber, except that silver reflects
8_mirror_drying.jpg (43.53 KiB) 已瀏覽 9459 次
The silver layer was being dry polished by a Chamois skin (a process called silver burnishing ). If we had used pure disitill water for the final rinsing stage this procedure could be avoided.
9_silver_burnishing.jpg (55.98 KiB) 已瀏覽 9459 次
最後由 Chanlunlun 於 週六 12 6月, 2004 17:58 編輯,總共編輯了 1 次。

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文章 Chanlunlun » 週六 12 6月, 2004 17:49

more photo
The finished silvered mirror. The silvering was a total success this time. The silver layer was white and shinny, at least at this moment.
10_silver_finish.jpg (47.21 KiB) 已瀏覽 9457 次

文章: 5
註冊時間: 週一 13 10月, 2003 21:11

文章 wilsonclass1d » 週六 12 6月, 2004 18:47

Chan sir..........
my trouser 點算呀????????
add conc. lemon ar???????

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註冊時間: 週六 28 6月, 2003 12:03

文章 Wongsir » 週六 12 6月, 2004 22:45



:shock: :shock: :shock:


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