Silver

Silver is a metallic chemical element with the chemical symbol Ag (Latin: argentum, from the Indo-European root *arg- for "grey" or "shining") and atomic number 47. A soft, white, lustrous transition metal, it has the highest electrical conductivity of any element and the highest thermal conductivity of any metal. The metal occurs naturally in its pure, free form (native silver), as an alloy with gold and other metals, and in minerals such as argentite and chlorargyrite. Most silver is produced as a by-product of copper, gold, lead, and zinc refining.

Silver has long been valued as a precious metal, and it is used to make ornaments, jewelry, high-value tableware, utensils (hence the term silverware), and currency coins. Today, silver metal is also used in electrical contacts and conductors, in mirrors and in catalysis of chemical reactions. Its compounds are used in photographic film and dilute silver nitrate solutions and other silver compounds are used as disinfectants and microbiocides. While many medical antimicrobial uses of silver have been supplanted by antibiotics, further research into clinical potential continues.

Cleaning

 * Mechanical


 * Chemical

1.Saponaria Officinalis(soapwort) extract

100 gms soapwort root/ 1 lit water

Pour boiling water on dry root,cover and after 10 minutes you can use it.Fresh  solution is  pH neutral.This solution can be used for removal of dirt and thin corrosion layers(use only fresh solution!). When object is clean rinse well.

Do not use on archaeology objects!

2.Ammonium Thiosulphate solution

150 gm ammonium thiosulphate

10 gm nonionic detergent

1 lit water

Immerse object in solution. Dissolves thick chloride layers and sulphide! Rinse Thoroughly!

Do not use on archaeology objects!

3.Thiourea based solution

80-100 gr thiourea 1 lit water 15 mll HCl

Immerse objects in solution.When cleaned,rinse well! It removes sulphide,chloride and oxide layers! Between immersion steps you can brush object with soft toothbrush dipped in precipitated chalk and water-pressure on object must be very gentle! Try to avoid any contact with solution or powder-thiourea is carcinogenic compound! Do not inhale rotten eggs smelling gas formed during process-it is toxic and flamable! There are other variants of formula,first one use phosphoric acid(according to G.Wharton), second nitric acid(according to one USA patent),last variant can be used on chromium plated objects too. Do not use on archaeology objects!

4.Precipitated Chalk and Water Paste

mix chalk and water Rubb on object,when it is clean rinse well. Few drops of ammonia can be added too! Do not use on archaeology objects!

5.Sodium thiosulphate solution

300 gm sodium thiosulphate

1 lit water

Immerse objects in solution!When it is clean rinse well! Can be used on other precious metals too! Do not use on archeology objects!


 * Electrochemical

Electrolytic cleaning

2-5% NaOH solution

Stainless steel anode,up to 12 v,cca.1-2A/dm2

Immerse object connected to negative terminal of current source ,stainless steel anode conected to positive terminal must be immersed in solution before start of cleaning. Instead NaOH sodium or potassium carbonate or natrium tetraborate can be used! Do not use on archaeology objects!


 * Ultrasonic

Thiourea based solution can be used for ultrasonic cleaning too (80 gms thiourea/50 ml phosphoric acid/1 lit water - according to Bruno Muhlethaler,1 minute immersion,then rinse well and repeat if needs).


 * Laser

There are well documented examples of laser cleaning of  silver  objects:

1.Siano,S.;Salimbeni,R. Advances in Laser Cleaning of Artwork and Objects of Historical Interest: The Optimized Pulse Duration Approach,Acc. Chem. Res., 2010, 43 (6), pp 739–750

2.A.Gervais, M. Meier, P. Mottner, G. Wiedemann and W. Conrad, et al.:Cleaning Historical Metals: Performance of Laser Technology in Monument Preservation Springer Proceedings in Physics, 1, Volume 116, Lasers in the Conservation of Artworks, Part I, Pages 37-44,2007.

Silver plating - restoration
Silver plating /I

40 gm silver chloride

20 gm potassium carbonate

200 gm potassium ferrocyanide

1 lit water

stainless steel anode,cca.2 v

0,5-1 A/dm2

Dissolve ferrocyanide,add carbonate,as last add silver chloride.Boil it 30-180 minutes. Can be used on copper and copper alloys,tin,zinc,iron. Can be used for electroforming.

Use it only on damaged parts of object!

Silver plating/II

23 gm silver diphosphate

100 gm potassium diphosphate

23 gm ammonium carbonate

1 lit water

stainless steel anode

Dissolve potassium diphosphate in hot water,when it is dissolved add carbonate ,and when it is dissolved add silver compound.Object(grease and oxide free!) must be connected to negative terminal of current source,anode to  positive. When silver layer is formed polish it with fine brass wire brush immersed in soapy water.Can be used on copper and copper alloys.

Use it only on damaged parts of object!

Immersion silvering

15 gm silver nitrate

10 gm ammonium chloride

30 gm sodium thiosulphate

1 lit destilled water

Dissolve nitrate in 50 mll water,when it is dissolved add ammonium chloride dissolved in same  amount of water. Dissolve thiosulphate in 900 mll water and then mix both solutions. Immerse grease and oxide free object in solution,when silver layer is formed, rinse well.Can be used on copper and its alloys.

Use it only on damaged parts of object!

Immersion silvering/II

26-52 gm silver nitrate

60-240 gm citric acid

40-80 gm thiourea

1 lit water

18-20 C temperature

Can be used on copper and its alloys.Try to avoid any contact  with  solution, thiourea is cancerogene compound!

Use it only on damaged parts of object!

Paste silvering

10 gm silver chloride

20 gm sodium chloride

20 gm cream of tartar

Mix all ingredients to thick paste. With piece of cork(or leather,or rag) take some paste  and rub it on grease and oxide free object. When silver layer is formed rinse well,and then polish it with fine brass wire brush previously immersed in soapy water. Immidiatelly lacquer or wax it. Can be used on copper and its alloys.

Use it only on damaged parts of object!

Leaf sivering

Silver or imitation silver leaf can be used.Silver powder can be used too.Easy to apply,easy to remove.

Special paints

MirraChrome(R) paint can be used.

Cleaning
On archaeology objects we  must prefer mechanical cleaning methods!
 * Mechanical cleaning

Structural consolidation

 * Mechanical joining
 * Soldering
 * Welding
 * Gluing/cementing

Stabilization

 * Corrosion inhibitors
 * Conversion coatings

Clearcoats

 * Paraloid B 72
 * Nitrocellulose lacquer

Waxes

 * Renaissance Wax
 * Cosmolloid 80 H