The chemical reactions are a process of ‘ionic exchange’ – this means that an ion of the base metal is exchanged for a modified ion of a compound formed in solution by a reaction of that metal.  For example, a copper ion is liberated from the surface of the metal being treated by galvanic action, forms a modified ion which redeposits itself back on the surface – hence ionic exchange.  The nature of the complexed ion and the subsequent structure of the deposit will determine the colour or hue of the modified surface.  This is how the antiqueing effect occurs.  Over a time, free ions will build up in the solution which in time will change the balance of the solution and effect the colour results deeming the solution spent or exhausted.  The free ions will build up whilst at the same time the other constituents will be depleted; this will render the solution out of balance and will require disposal of the bath and recharging with a fresh solution.

Most metals can be antiqued but the effects are limited to those effects, which naturally occur in the environment.  All metals patinate in different ways – iron and steel will either oxidise to a red rust or sulphurise to a black, depending upon the environment to which it is exposed.  Zinc and aluminium will oxidise to a white powder, and silver will turn black in the presence of sulphur dioxide, carbon dioxide or nitrogen oxide to form silver oxide and silver nitrate salts.

Copper and its alloys demonstrate the widest variance because the wide variation in the colours of the various oxides and compounds which form on copper.  These vary from the blues and greens of verdigris, to the bronze colours exhibited by the oxides, dioxides, carbonates, sulphides and various other airborne agents.  It is commonly reactive in the presence of chlorine and sulphur.  Certain reactive agents have a certain affinity for particular metals; nickel for example is a noble metal, which will be effected by sulphates but gold being the most noble of metals will not be affected at all.  It follows therefore that when synthesising these colour effects for commercial purposes that the chemistry must follow the natural rules – certain metals will be affected in certain ways by certain chemicals.

We can treat Copper Alloys to give either the aggressive effects of the verdigris greens and blues or the gentler patinated effects of the reds or brown/grey bronzes.  The patinas vary from the light oxide effects of the reds, through the light ‘Old English’, medium ‘Old English’, through medium Bronze Antique and dark Bronze Antique to almost black.  The nature of the colour effect will depend upon the texture of the metal surface to be treated, the choice of acid to initiate the reaction and the chemical combinations to modify the structure of the reactive deposits.  Generally the light effects are activated by lighter acids and the darker ones by heavy acids.  For medium bronze antiques, ARMATONE “CM” and “CNG/F” are our standard processes for use on Copper, Brass and Bronze and cover the ‘medium antique bronze’ spectrum of our antique range.  “CM” is described as a grey/brown as opposed to the “CNG/F” process which is a red/brown which gives a more chocolate brown type of colour as would be evinced by the effects of patina on a copper rather than a grey/brown of a brass background.  The light ‘Old English’ patinas are represented by our ARMATONE “CFB” and “CFB-2” processes and give effects which are best described as ‘buff’ colours rather than browns and when used on antique door furniture, match very well with the light oak and medium oak doors for which they are formulated.

Copper and its alloys can be affected by hydrochloric, Hydrobromic, phosphoric, sulphuric and nitric acids.  These mineral acids will also affect ferrous metals.

Nickel is not usually patinated, but recently there has been a move towards black nickel effects.  Nickel as a metal is not effectively activated by phosphoric or hydrochloric acids but will react with sulphuric to form nickel sulphate.  It follows then that nickel requires a sulphuric activator to establish a base for subsequent reactions.  Sulphuric when used as the activator on nickel or the copper alloys will result in the darker effects.  The lighter effects on copper alloy are affected by the phosphorics or hydrochlorics.  Our ARMATONE “BN” process is formulated for use on nickel or nickel-plated articles and can be used either as a dip process or for small components as a barrelling process.  When used on copper alloys, “BN” will tend to the darker end of the bronze spectrum because of the sulphuric element.

A dilute sulphuric acid may also be used as a surface activator on passive nickel components in preparation of subsequent blacking process, or alternatively a safety pickle (ADAS, dry acid salt) may benefit for ease of use.

We supply two types of process for ferrics.  The rust effect, which is preferred on cast iron garden furniture and which is similar atmospherically to the verdigris effects on copper alloys in that the resultant surface is due to a combination of corrosion and metal salt formation.  This is represented by our process ARMATONE “FeDOX” and components are usually waxed, oiled or lacquered after treatment.  The other processes are cold (or room) temperature blacking processes and are popular with wrought iron manufacturers for use directly on iron and steel.  The most extensive use however is on small highly engineered components and machine tool parts.  This is represented by our ARMATONE “BS” and ARMATONE “BS2” processes.  Again, components are usually sealed with wax, oil or lacquer after treatment.  The “BS2” process has also been found to be very effective for a brown black effect on brass.  There are no major costs involved in setting up a process line and installations can be as small or as large as is required, unlike the hot processes which present altogether a much larger commitment in equipment terms.

There are many instances where the same solution can be used for differing metals.  The individual ARMATONE processes are designed to give specific colour effects on specific or individual metals.  However, each process will have a non-specific effect on all other metals that may or may not be covered in the Product Information Sheets provided.  What must be avoided however is the practice of using one process in one tank for the treatment of both ferrous and non-ferrous metals.  When treatments are carried out, the reactions will leave free ions in the solution that will build up and compromise the colour effects on each type of metal that may subsequently be treated in the tank.  For example, ferrous ions will migrate onto the copper being treated and the copper ions will affect the deposits on the ferrous components.  If a process is to be used for both metals then separate tanks should be employed.

Remember, the results of any chemical treatments are only as good as the pre-treatment.  All metal surfaces generally will be contaminated with either oils, greases, fats, waxes and oxides – these must be removed.  Detergent or hot alkaline cleaners will remove the oils and fats, and a sour rinse will remove the oxides.  The degreasers – detergents and hot alkaline cleaners – are represented by our ARMACLENS range of processes.  The deoxidisers for making up the sour rinse is our ARMADOX “W” process which is a hydrochloric acid mixture with wetting agents and is used at 5 – 10% strength, and ARMADOX No.2 which is a sulphuric based version.  The use of these pre-treatment processes will ensure good effective reactions and non patchy, even results.

It is not a good idea to contaminate the environment with untreated chemicals.  The environment inspectors do not like strong acids, strong alkalines or dissolved metals to enter the drainage system, nor processes which deplete oxygen from rivers or water courses endangering aquatic life forms.  Provided two rinses are used after each treatment, i.e. a still rinse and a running rinse, no great problems will be experienced.

Based upon our own tests in conjunction with various water authorities in relation to the installations we have carried out, the still rinses will contain 99.99% of any chemical carry over.  The running rinse will give immeasurably low readings sufficient to enable it to go straight to drain.  The still rinse will contain dissolved metals that can be settled out by raising the pH to 9.5 – 10.5 by the addition of caustic soda.  The solution is first transferred to a holding tank, the caustic stirred in and the pH raised to 10.5.  The metals will come out of solution and gradually settle to the bottom of the tank; this can be accelerated by the addition of a polymer flocculant such as our ARMATERIC “77”.  The clear water can then be run off into a second tank and the pH adjusted to 6.5 – 9.00 pH with hydrochloric acid.  This can then be introduced to the effluent/drain stream and be disposed of by dilution with clean clear water.  The metallic residue from the settlement tank can be removed and caked or dried, to be disposed of according to local requirements.  If the same still rinse is used both for the alkaline degreaser and the antiqueing solution, one will to a degree neutralise the other.  Make a point of checking the pH on a regular basis and keep a running record.  The inspectorate will be impressed if you can demonstrate vigilance by maintaining records.

Please ensure that you are up to date with all relevant Technical Information Sheets and Health & Safety Information Sheets; if you are short of any, contact your supplier immediately.  The safety information sheets should form the basis of your Risk Assessments File.  Please copy any information provided into more than one file to ensure you cover for any lost or mislaid information.

In some circumstances it is impossible to immerse components into the antique solution, such as the component is too large, long, bulky or needs to be done in situ. In these instances it is possible to apply an antique finish by hand, using a sponge or brush etc.

Firstly the solution should be made up to between 5% and 20% strength, this can be altered depending on your preferences, it may be better to dilute even further which will allow more time to cover the whole surface. The component should be thoroughly cleaned so there are no contaminants on the surface, any contaminants (oil, grease, finger marks or oxides) will form a barrier between the solution and the component therefore leaving a patchy effect after antiqueing. Once the component is “Chemically Clean” immerse a scouring sponge into the solution then, using the scouring side, rub over the surface of the component making sure the whole of the surface is covered as quickly as possible, ensure you use plenty of solution so it does not dry out on the surface. Once the whole surface has been covered turn the scouring sponge over to the sponge side and continue applying the solution over the whole surface until you achieve the desired colour, you will need to keep going over and over the surface, this may take upto 10 minutes. When the correct colour has been achieved rinse thoroughly to ensure there is no residual acid left on the surface (Do not wipe water over the surface as this just dilutes and moves the acid around the surface and will cause problems in the future). The components will then need drying and sealing.

This method places a great deal of emphasis on the operative applying the solution and may take some practice to perfect, however once the operative has practiced a few times and realises what is happening on the surface and gets the timing correct it will become fairly straight forward.

Finally, this method is best to achieve the darkest colour the solution will go, however once the component is rinsed thoroughly it is possible to relieve the surface, using scotchbrite pad, or wet pumice powder and a sponge to rub back the surface to a lighter colour. (DO NOT use wire wool as this will cause an adverse reaction with the brass component)

Please contact us for health and safety data sheets.