Antique and patina finishing on metals
Updated: Dec 14, 2022
Focal is a specialist when it comes to different finishes on metal. We have been utilizing a number of different processes for years and are constantly testing and refining these processes.
The patina process is something that we absolutely love to do and it is something that is subjective to the client. There is not necessarily any wrong results, just differences of opinions and preferences.
Patina is a naturally occurring process that happens over time to metal when exposed to air. The metal will oxidize and change the look of the surface. With steel, oxidizing comes in the form of rust. With brass and copper, this comes in the form of brown, black or green surface depending on the enviroment and what the metal has been exposed to.
We can expedite this oxidizing process with special acids and get the metal to be the colour that the client wants and then we seal this to lock the colour in. There are a few different ways that we can seal in the patina with either bees wax, a matt or satin clear lacquer, or a matt clear powdercoat.
How we patina brass and copper:
First we need to make sure that no skin is exposed and that we have all of our safety gear on including gloves, respirators, and eye protection and that we are in a well ventilated area-These acids are nasty!
The acid needs to be diluted with water- We generally dilute it 50% remembering the golden rule of working with acids- always add acid to water and never the other way around.
Before applying any acid to metal, you will need to make sure that the metal has been thoroughly cleaned. Generally we will first use scotchbrite as this helps the patina bite in to the metal and then we will use a thinner. Any finger marks or other imperfections will have the patina reacting differently in these areas.
Depending on the situation will change how we apply the patina. If we are doing panels, then we will apply it with a spray gun with the panel lying flat. Any pooling or running of patina will result in different reactions showing up in those areas. We have found that you need to act quickly as the acid is corrosive and can easily damage the gun. A gravity fed gun with a plastic cup works best as the plastic will not corrode however the insides of the gun still can.
Other ways to apply the acid can be with a brush or a rag that has been sitting in the solution.
Whatever way that you choose to apply it, the number one thing that you need to remember is that you will apply it, and then quickly wipe it back off with a clean rag.
You may need to do this process 10-20 times until you get the desired colour. This is the part where you need to use your judgment as there are a lot of factors that can affect the outcome of the colour and even if you do the exact same process, the next part may not be the same and you may need to do this more or less times.
Once you have achieved the colour that you want, you will need to use water over the area to neutralise the acid reaction.
It is best to seal the metal as soon as possible once you have finished as even though the acid has been neutralised, it can still change.
After you have finished, make sure that you dispose of all of the chemicals correctly and do not put them down the sink.
Patina/force rusting steel:
A lot of clients love the cor-ten steel look with rusted steel. This can be done will all of types of steel. The difference with cor-ten is that the once the initial rust takes hold, it will protect the rest of the steel. With mild steel, it will continue to rust.
Steel after spirit of salts has been used.
Steel once it has been force rusted.
How to force rust steel:
Steel over 3mm thick will always come with a black layer called mill scale. This happens in the manufacturing process in the steel mill. A lot of people love this look as it gives the steel a beautiful and natural look. This mill scale also protects the steel from corrosion (to a point).
To rust steel, this layer of mill scale needs to be removed. To do this, we use a product called 'spirit of salts'. This is a mixture that contains hydrogen chloride and water. Like the patina, it is a nasty chemical that requires protective gear.
Coating the steel in this chemical will quickly start to remove the mill sale
Once the mill scale has been removed- generally it should be within 30 minutes, you can wash it off.
After the mill scale has been washed off, the quickest way to get your items to rust it to leave them outside in the elements. They will be fairly rusted overnight however, the longer you wait, the more consistent the rust colour will be.
After you have waited a few days and are happy with the colour, you can wipe off the excess rust with a rag and then install your parts
The thing that we love about these processes is that it is completely subjective. You can have a lot of fun experimenting with different finishes and patterns.
An example here is building layer upon layer of patina and then using scotchbrite to take off little bits here and there which gives it a naturally tarnished look- have fun!
-George