Iron

Iron is a chemical element with the symbol Fe (Latin: ferrum) and atomic number 26. It is a metal in the first transition series. It is the most common element in the whole planet Earth, forming much of Earth's outer and inner core, and it is the fourth most common element in the Earth's crust. It is produced in abundance as a result of fusion in high-mass stars, where the production of nickel-56 (which decays to iron) is the last nuclear fusion reaction that is exothermic, becoming the last element to be produced before collapse of a supernova leads to events that scatter the precursor radionuclides of iron into space.

Like other Group 8 elements, iron exists in a wide range of oxidation states, −2 to + 6, although +2 and +3 are the most common. Elemental iron occurs in meteoroids and other low oxygen environments, but is reactive to oxygen and water. Fresh iron surfaces appear lustrous silvery-gray, but oxidize in normal air to give iron oxides, also known as rust. Unlike many other metals which form passivating oxide layers, iron oxides occupy more volume than iron metal, and thus iron oxides flake off and expose fresh surfaces for corrosion.

Cleaning

Mechanical

• Microsandblasting
• Dry ice blasting
• Scalpel
• Glass fibre brush
• Water or oil and abrasive particles

Chemical

1.Ammonium citrate solution

50 gm citric acid

1 lit water

Add some ammonia 25%,ph must be 3,5!

Immerse objects in solution,when it is cleaned rinse well. Hot solution work faster(80 C). Brushing with precipitated chalk and water may be helpful,you can use fine steel wire brush too.

Do not use on archaeology objects!

2.Phosphoric acid solution

phosphoric acid 10-20%

up to 1% gelatine can be added

Immerse objects in solution,when they are clean rinse well.Brushing with fine steel wire brush can be helpful.

Do not use on archaeology objects!

3.EDTA based solution

40 gm EDTA

1 lt water

pH must be corrected to 5,5(with citric acid and NaOH)

Immerse object in solution,when it is clean rinse well! Can be used on objects with inlays. Do not use on archaeology objects!

4.Thioglycolic acid solution

thioglycolic acid 3-3o%

pH must be 7

Effective neutral rust remover.Bad smelling! When object is clean rinse well!

Do not use on archaeology objects!

5.Petroleum based rust softener

1 lit petroleum

20-30 gm parafine

Immerse object in solution,duration depends on amount of rust(up to 3 days!). Rust must be removed with steel brush or finest steel wool,or old rag.

Specially for blued , browned or blackened iron or steel!

6.Solution for cleaning painted iron

10 mll ammonia 25%

90 mll propyl alcohol

900 mll destilled water

Solution can be gelled with wallpaper glue(methylcellulose based). Pieces of cottonwool moistened with solution can be wrapped with plastic foil(to minimize evaporation) too. Ethyl alcohol can be used instead propyl. Specially for slow,controlled paint removal of paint layers! Stronger solution can be used too,but be careful(20 mll ammonia/180mll propyl/800 mll water)!

7.Mixed organic acids

47,5 gms citric acid

47,5 gms sodium gluconate

4,9 gms tartaric acid

1 lit water

Immerse objects in cold or hot (80 C) solution,then rinse well.

8.Polymethacrylic acid

100-150 gm polymethacrylic acid

1 lit water

pH must be corrected with ammonia to 4,5-5,5

According to Russian literature polymethacrylic acid can be used as rust remover.It must be brushed on object,when dry brush it off.Repeat if needs.

Electrochemical

Electrolytic cleaning

NaOH 2-5 %

current density-at least 1 A/dm2

up to 24 v

stainless steel anode

Immerse object( connected to negative terminal of current source!) in solution, anode must be immersed in solution before!

Do not use on soft soldered ,tin,zinc or chromium plated objects!

Do not use on objects with elastic parts!

Do not use on archaeology objects!

Ultrasonic

sodiumhydroxide 5-19 gms

sodium carbonate 15-25 gms

trisodium phosphate 49-60 gms

water 1 lit

Immerse objects in solution 2-5 minutes,then rinse and continue treatment if needs.

Laser

There are well documented examples of laser cleaning iron and steel!

Structural consolidation

• Mechanical joining
• Soldering
• Welding
• Gluing/cementing

Stabilization

1.Tannic acid treatment

200 gm tannic acid

150 mll ethanol

1 lit distilled water

Immerse objects in solution(dry it-30 C temp.,72 hours!).You must brush dry object, after brushing you can wax or lacquer it.

2.Tannic acid/Phosphoric acid mixture

20 gm tannic acid

15-19 gm phosphoric acid

1 lit distilled water

Immerse object in solution or paint it with solution.Dry,wax,lacquer. It can be used on grease and oxide free objects,and rusted objects too.

Do not use on archaeology objects!

3.Tannic acid/Phosphoric acid mixture - russian formula

10 gm tannic acid

5 gm phosphoric acid

20 gm acetone

65 gm distilled water

Dissolve tannic acid in acetone,add phosphoric acid,add water.

4.Phosphating

2-3,5 gm primary zinc phosphate

0,5-18 gm primary calcium phosphate

1 lit distilled water

Before use add 4 gm sodium nitrate.Grease and oxide free objects must be immersed in solution(10-20 minutes). Dry,wax or lacquer.

Do not use on archaeology objects!

5.Phosphating /II

10 gm sodium hexametaphosphate

3,2 gm calcium chloride

0,05 gm sodium nitrite

1 lit water

That solution can be used on lightly rusted surfaces.Colourless coating. Contact object/solution 60-120 minutes,temp.18-25 C/pH 5,6.

Protective coatings

Clearcoats

• Paraloid B 72
• Paraloid B 67
• Paraloid B 44
• Paraloid B 48 N
• ORMOCER

Waxes

• Renaissance Wax
• Cosmolloid 80 H
• Dinitrol 4010

Oils

• DIY Mixture - 20 parts fish oil / 80 parts white spirit

Combinations

• Basecoat Paraloid B 72 + topcoat Renaissance Wax etc.

Conservation- archaeology objects

Cleaning

• Mechanical

-microsanblasting

-scalpel and scraper

-steel or ceramic burs and cutters

-grinding wheels

-glass fibre brush and pen

• Chemical - Not recommended!
• Electrochemical - Not recommended!
• Ultrasonic - Not recommended!
• Laser

Structural consolidation

• Gluing/cementing

Stabilization - archaeology objects

• Chloride removal

1.Alkaline sulphite treatment

63 gm sodium sulphite

20 gm NaOH

1 lit distilled water

Dissolve hydroxide,add sulphite,add objects and close container tightly(stainless steel!). Solution(heated to 50 C!) must be mixed with magnetic stirrer. Process duration 7 days.Chloride level must be controled,and process continued for additional 7 days.Repeat chloride control and continue process if needs. When chloride level is acceptable we can rinse objects with water,after that with 3%barium hydroxide and then again with water. According to new literature much weaker solution can be used too(6,3 gm sulphite/2 gm xydroxide/1 lit water).Barium hydroxide rinsing can be ommited!Cold solution can be used too!

Do not use on tin plated objects or objects with traces of organic materials!

2.Electrolytic chloride removal

current density 0,25 A/dm2,2-4 v

stainless steel anode

distilled water

conductivity meter

water change every 6-48 hours

Objects must be placed between two anodes. Control conductivity every 6-48 hours. When chloride level is acceptable dry with infrared lamp,wax or lacquer. Marine finds must be first treated with 2-5% NaOH dissolved in tap water. When chloride level drop we can use tap water,and when we reach level that is same as tap water chloride level we can use distilled water.Last step is dehydration with acetone or alcohol,and waxing or lacquering.

3.Steam and hot water

Objects must be steamed for 3 hours,then 3 hours treated in boiling water(distilled water). Repeat until chloride level is acceptable. Dry with infrared lamp,then wax or lacquer.

4.Ethylene diamine

Immerse objects in 2% NaOH,first change solution every week,then every month. After that step treat with 5-20 % Ethylene diamine(50 C).Duration of NaOH treatment up to one year,second step up to 4 months. Chloride level must be under 50 ppm(20 ppm best!). Ethylene diamine is flamablle,try to avoid any contact with solution! According to some new russian sources instead Ethylene diamine we can use triethanolamine/dimethyl sulphoxide mixture(1/1).

• Rust converters

Tannic acid treatment

200 gm tannic acid

150 mll ethanol

1 lit distilled water

Immerse objects in solution(dry it-30 C temp.,72 hours!).You must brush dry object, after brushing you can wax or lacquer it.

Protective coatings

• Clearcoats
• Waxes
• Combinations

Further reading

1.Selwyn,L. Metals and Corrosion-A Handbook for Conservation Professional,Ottawa 2004.

2.D.A.Scott Iron and Steel in Art - Corrossion,Colorants,Conservation, London 2009.

3.Scott,D.A. Metallography and Microstructure of Ancient and Historic Metals,Santa Monica 1991.

4.Scott,D.A. Ancient and Historic Metals-Conservation and Scientific Research,Santa Monica 1994.

5.Dillman,P.;Beranger,G.;Piccardo,P.;Matthiesen,H. Corrosion of metallic heritage artefacts-Investigation,Conservation and Prediction of long term behaviour,Cambridge 2007.

6.Cronyn,J.M. The Elements of Archaeological Conservation,London 1990.

7.La Niece,S.;Craddock,P. Metal Plating and Patination: Cultural,Technical and Historical Develpoments,Boston 1993.

External links

• UCLA metals course-archived presentations

• World Steel Association

• METAL 2004-proceedings of conference

• CONSIST project

• International Conference on Strategies for Saving Indoor Metallic Collections,Cairo 2007.-conference papers

• Iron conservation,part I

• Iron conservation,part II

• Archaeological Iron Conservation Colloquium 2010 Abstracts:
  • http://www.iron-colloquium.abk-stuttgart.de/Documents/Tagungsband_session_1.pdf
  • http://www.iron-colloquium.abk-stuttgart.de/Documents/Tagungsband_session_2.pdf
  • http://www.iron-colloquium.abk-stuttgart.de/Documents/Tagungsband_session_3.pdf
  • http://www.iron-colloquium.abk-stuttgart.de/Documents/Tagungsband_session_4.pdf
  • http://www.iron-colloquium.abk-stuttgart.de/Documents/Tagungsband_postersession.pdf

• Canadian Conservation Institute Notes:
  • 9/6 Care and Cleaning of Iron
  • 9/8 Mechanical Removal of Rust fom Machined Ferrous Surfaces
  • 9/5 Tannic Acid Treatment

• Bevilacqua,N. Materials for iron conservation

• Armas protohistoricas con magnetita

• Conservation of iron and steelwork in historic structures and machinery/Maintenance handbook