Patina 101

[Larry Davis]

I have noticed that in several threads there were questions on the patination or colouring of metals. Having had well over 30 years of experience with these techniques, I thought that I might share a few recipes with the members.

But before I do, I want to say that I do not take any responsibility for any personal or property damage when someone attempts to prepare or use these recipes.

Most recipes are quite safe when done with a moderate amount of common sense and a healthy regard for safety. WEAR EYE PROTECTION and use an appropriate NIOSH-RATED RESPIRATOR! PLEASE!

I feel that brasses and copper alloys would be the most common metals to be patinated by the members of this group, so I’ll try to stick to chemicals that are easily obtained and easy to use.

What is a patina?

A patina is the naturally- or artificially-produced film or layer of oxidation resulting from metal coming into contact with acid-based chemicals.

With certain chemicals and combinations of chemicals, one can achieve a wide range of colours: greens, reds, browns, blacks in varying shades..

Basic Equipment:

• Chemicals. Find out what you need and lay it out before you start.

• Water. I always use distilled water with these recipes, as it will not introduce any minerals or metals to the mixture, and gives the most consistent results.

• Plastic or glass containers. Use ones with non-reactive lids.

• Scales. Or some other means of measuring volumes. These are optional. With experience, I have gotten to the stage were I never use them anymore.

• Torches. Propane is good. You want to be able to produce temperatures over 212 degrees F.

• Applicators. Brushes, sponges or spray bottles.

• Cleaning stuff. Soaps, solvents, Scotch Brite abrasive pads, rags, etc. I tend to stay away from steel wool, as the small steel fragments can contaminate a patina.

• Sealants. Waxes such as Treewax or Johnson’s paste wax (the best) preserve the patina. Tung oil can be used as well. NEVER, NEVER seal an artefact with lacquer of any sort. If the lacquer is scratched, the metal surface is exposed to the atmosphere, and the spot will oxidize. The oxidation will creep under surface of the lacquer and spoil the patina. Then, the only way to fix the spots will be to remove all the lacquer. What a pain in the ass!

• Safety Equipment. Rubber gloves, eye protection, and most importantly, a PROPER RESPIRATOR. I cannot emphasize this enough!



METHODS USED IN PATINATION

The Cold Patina (no torch used)

This is usually done by immersing the object in a bath of chemicals. The water temperature can be anywhere from cold to hot, though some immersion techniques require boiling the solution.

You can even achieve a cold patina by urinating on your artefact, if you’re so inclined.


The Hot Patina (with direct flame)

This technique requires that the piece be heated to around 212 degrees F. When a drop of water is dropped on the metal, it should vapourise; if it dances about the surface, in a ball, the metal is too hot and the patina will not stick properly.

The chemicals can then be applied with brush, sponge or spray.


THE PRELIMINARIES

Before you start, the most important step is to clean the artefact to be patinated.

First, scrub the piece well with a strong soap or detergent, followed with a solvent such as mineral spirits or methyl hydrate.

Be sure to remove all the old oxides, wax and grease from the surface. Wear gloves when you do this, as your hands will deposit oils as well. Dry the piece off.

When you are satisfied that it is clean, proceed to the next step. Remember, the patina will not work anywhere there is dirt or grease—so keep those gloves on.




PATINATING BRASS & COPPER

I’m going to stay away from the more dangerous acids (such as nitric or sulphuric) and stick with the simpler, safer recipes. Unless you are planning to patinate an over life-size bronze, simple is always best.

Remember, always neutralize the finished patina with a bath of baking soda in water, and rinse well before drying and waxing. If you don’t, the acids will just keep on eating your artefact!
Also, if you find that you don’t like the colour you have produced, just remove it with an abrasive or sand blaster and start again. If you have already waxed it, remove the wax with a solvent or burn off the wax with a torch before starting a new patina.

Waxing the item. This process is almost always done with the piece hot—not to the point of making the wax ignite—but just so it melts into all the cracks and details and produces a thin, smooth skin. You don’t need a lot, but it has to be completely coated. When the piece is cool, polish it with soft cloth, and perhaps bring up a few highlights in the metal by polishing details with a Scotch Brite pad or fine sand paper.


RECIPES

1. Gun Blueing.

The simplest (and the most easily obtained) way to patinate brass and copper based artefacts is with commercial gun blueing solutions.

Start with a volume of water just large enough to immerse your item. Warm water works faster.

Thoroughly wet the piece in water to drive off any air bubbles. The patina will not colour under the bubbles, resulting in bare spots.

Immerse the piece in the water, and slowly add small amounts of gun blue to the water until the artefact starts to brown. Be sure to gently and continuously agitate the solution over the piece.

When the piece has developed a blackish skin or ‘fuzz’, take it out, and with a soft brush (like a toothbrush), wash it under water to see if it has developed the colour you want.

If you want it darker, re-immerse it and repeat the process.

Neutralize the piece with a wash of baking soda and water and rinse well. Dry the item completely and seal the patina with your choice of either a wax or Tung oil.




2. Brown (light to dark)

Chemicals: Ferric Nitrate - ½ teaspoon
Distilled water - 1 pint

Method:

Heat the metal until a drop of water sizzles on its surface.

Brush or spray on the solution while constantly reheating the metal, until you achieve the desired colour.

You can get any shade from a chestnut red to a dark brown, but try not to burn it by applying too much heat.


3. Brown to Black

Chemicals: Potassium sulfide (aka sulphurated potash or liver of sulphur) - a flower or lump the size of a nickel (it has to be fresh, or it won’t work).
You can tell if it is fresh by the colour: yellow is fresh, dusty white means it’s garbage.
Distilled water - 1 pint

Method:

Use the hot process or immerse in warm solution.

Do this outside as it smells strongly of rotten eggs (the sulphur you know!)


4. Greens

Chemicals: Cupric Nitrate – 1 teaspoon
Distilled water - 1 pint

Method:

Apply to heated metal with brush or spray method. Build up applications to the desired depth and colour.






5. Olive Green

Chemicals: Cupric Nitrate – ½ teaspoon
Ferric Nitrate – ½ teaspoon
Distilled water – 1 pint

Method:

Heat metal and apply.



6. Cold Process Green.

Chemicals: Cupric Nitrate – 40 gm
Ammonium Chloride – 40 gm
Calcium Chloride – 40 gm
Distilled Water - 1 Litre

Method:

Use the cold process. Several applications are needed.

(One can also get a great brown green by urinating on the piece at interval—and it smells like it for ever and ever.)


7. Reddish brown (cast brass)

Chemicals: Cupric Sulfate - 125 gm
Sodium Acetate -12 1/2 gm
Distilled water - 1 Litre

Method:

Boiling immersion for 10 – 15 minutes. The colour will develop after 10 – 15 minutes.


8. Red (cast brass)

Chemicals: Cupric Nitrate - 8 oz
Oxalic Acid - 8 oz
Distilled Water - 1 gallon

Method:

Heat metal and apply.

Further Reading

For more recipes and techniques, check out Richard Hughes’ and Michael Rowe’s book, ‘The Colouring, Bronzing and Patination of Metals’.
I’ve been using it for years. It has lots of colour plates.

Good luck, and remember to patinate outside!

[Arik Estus]

Larry,
Thank you. Some of these I hadnt seen before.
Very interesting. I will have to print it out for referance.

Jerry asked me about patinating Titanium. Any ideas or advice? Thanks.

[Larry Davis]

Arik,
We used to use heat (torch or kiln), an electrical current or anodising to colour titanium. Some of the chemicals were as mundane as TSP, salt, lemon juice and baking soda with a 24 volt current.

I could not find my notes so I borrowed the following from www.azom.com

There is also an excellent artical at efunda.intota.com under 'Titanium Anodizing' by Mr. Edward P Short.

Try doing a Google search on "titanium anodizing", there is a great deal there.

"Acid Anodising
Contrary to popular belief, acid anodising of titanium which thickens the oxide film confers only a minimum improvement to wear resistance. The anodic film also serves to reduce the inward diffusion of oxygen at elevated temperature and of hydrogen under conditions of galvanic charging. Many electrolytes are effective; 80% phosphoric acid + 10% sulphuric acid + 10% water produces a sound coherent film with potential raised from 0 to 110v over ten minutes. Galling can be significantly reduced by acid anodising for example on threaded components, by conjunction with compressive surface treatment and with a dry film lubricant. Ti-6Al-4V bolts used on the successful Heidrun riser had an epoxy polyamide molydisulphide coating applied over a peened and anodised surface.

Alkaline Anodising
Thicker oxide films able to withstand relatively higher loadings are produced by alkaline anodising processes such as TiodizeR. Long established alkaline base proprietary finishes such as CanadizingR control the oxide film thickness and density so that one or more of a series of dry film lubricants may be applied and ‘locked-in’ to the surface. Canadized coatings were used successfully to prevent galling at the joints and in the drive shaft of the titanium core sample drill tubes used in NASA’s exploration of the moon.

Colour versus Anodised Film Thickness
Progressive thickening of the oxide film by anodizing results in colour changes due to refraction of light. This effect has been used selectively for component identification, but more imaginatively for colouring titanium sheet to produce ‘paintings’, and ornamental jewellery. Various electrolytes are suitable, but 3 - 5% trisodium phosphate in distilled water is commonly used. Colours produced vary according to the electrolyte and the applied voltage."

Good luck.

[Jerry Bennett]

Thank you Larry!

I will file your info in my vault of “esoteric knowledge”. I can work the stuff, but I don't have much experience with coatings and finishes and the like. Thanks! Jerry

[Arik Estus]

Well, I am glad to see Jerry found it. I put in all sorts of
words but not anodizing. My bad. But, Larry isa good guy.
Two thumbs up.

[Larry Davis]

I wish I could have been more help, but it has got to be 20 years since I worked with titaniun and niobium.

I hesitated to give more information untill I found my notes.

But I'm glad what I found was of some help.

Larry.