Safety Emporium is a proud sponsor of this site.
	Home Page --> Tutorial Lesson 17, Silvering Glass (Advanced Topic)

Silver Plating - The Brashear Process

The Brashear process is commonly used to silver the internal surfaces of Dewar flasks, which are evacuated double-walled vessels (much like a Thermos® bottle) used for handling and storing laboratory cryogens such as liquid nitrogen and liquid helium. The combination of the evacuated double-wall and silver mirror surface greatly reduce heat transmission from the inside to the outside of these vessels.

The chemistry of this process is described in the Tollen's test which is a physical method that tests for the presence of aldehydes in an organic chemistry laboratory. A video of this process is available through the Royal Society of Chemistry.

Three Part Solution Mix for Internal Plating Solution 1 2 liters distilled water, 50 grams silver nitrate. Store in a dark glass bottle. Solution 2 2 liters distilled water, 90 grams potassium hydroxide. Solution 3 800 ml distilled water, 80 grams cane sugar, 100 ml ethyl alcohol, 3.5 ml nitric acid. Age 30 days or boil 30 minutes before using.

Solutions are used at the following ratio: 1 : 2 : 3 = 64% : 32% : 4% by volume. Cut out this handy table and stick it on your shop wall as a quick reference so you don't need to calculate volumes:

Solution Required	Solution 1	Solution 2	Solution 3
50	32	16	2
100	64	32	4
150	96	48	6
200	128	64	8
250	160	80	10
300	192	96	12
400	256	128	16
500	320	160	20
600	384	192	24
700	448	224	28
800	512	256	32
900	576	288	36
1000	640	320	40
1500	960	480	60
2000	1280	640	80

To use: First ensure that your glassware to be silvered is scrupulously clean. Then, add concentrated ammonium hydroxide dropwise to Solution 1 with stirring. It will form a precipitate with the first drop; continue adding until the precipitate clears. This should require no more than an eye dropper's worth of ammonium hydroxide for volumes up to ~500 mL. Add Solution 2 to Solution 1. The combined solutions will have a creamy white precipitate. Stir the solution and again add concentrated ammonium hydroxide dropwise until the solution is slightly cloudy. Pour the solution into the glass vessel to be silvered. Add solution 3 and stir/shake while the mirror develops.

Warning: Wear protective clothing and read the MSDS for all materials that you use. Promptly and safely discard unused mixed solutions.

We hope to post some pictures here that demonstrate a Dewar flask being made. Stay tuned!

This page and any associated material is copyright 2002-2013 by Joe Walas and/or ILPI unless otherwise stated. Unauthorized duplication or posting on other web sites is expressly prohibited. Send suggestions and comments (include the URL if applicable) to us by email. CAUTION: Be sure to read this important safety/legal disclaimer regarding the information on this page.