Brass is a great material and is used extensively as an architectural metal element, think door fixtures, lighting and more. Brass is an affordable metal alloy that mimics gold in appearance, has good resistance to corrosion and is reasonably priced, hence its popularity. So you’re obviously thinking of using brass outdoors and there is one question on your lips, does brass rust? Let’s jump into the science and find out!
Does brass rust?
If you’re being pedantic only iron or alloys that contain iron “rusts” as rust in the traditional sense is the iron oxide (rust) caused by moisture on iron. However, rust has come to mean a corroded surface on all metals in the popular consciousness.
So in one sense brass will not rust, brass is an alloy of copper and zinc (we have a similar article on does copper rust), as such it cannot rust to create iron oxide. However, it can tarnish, which for most homeowners with a beautiful brass object they want to protect is the same thing. Brass is quite a corrosion-resistant metal similar to other alloys like stainless steel.
This is not rust but a blue-green patina coating caused by a layer of various chemical compounds caused by a reaction between the brass and the elements it is exposed to. This can happen at different rates depending on the conditions the brass is exposed to. In a clean air environment, this will be a slow gradual process due to the reaction with carbon dioxide and water. It can however happen quicker in more polluted areas due to a stronger reaction with acidic rain caused by pollution from industry.
Overtime if not cleaned and polished the brass will turn a beautiful green, this is often the desired look and is left to occur naturally. This again happens with other similar metals like copper. Think of the statue of liberty as a perfect example, under her green exterior she is made from copper and would have originally been copper coloured when first constructed.
One interesting facet of the patina process is that once it is firmly established it actually helps protect the brass underneath from further corrosion. The patina film essentially acts as a natural coating and protects the brass underneath its surface.
This is the process where brass can slowly lose is zinc element and copper is left behind. This can have profound effects on the appearance of brass, leading to it turning more pinky and looking more and more like copper, for obvious reasons! At first, this will be a purely cosmetic effect, but if left untreated and allowed to get worse it can eventually lead to the weakening of the brass itself.
Dezincification is a particular problem when the brass is exposed to seawater, so if you live near the sea this will be an issue for any exposed brass you may have. However not only people living near the coast need to be wary. It has also been found to happen to door furniture such as kickplates which have been exposed to salty conditions thanks to the sold used to de-ice roads in winter.
If you are keeping your eye out for potential dezincification then the first clear sign you will see if a change of colour as the zinc leaves the alloy. It will start to go pinker and pinker as it turns into more copper than brass.
Dezinicifaction can be explained by the fact that zinc is more reactive than copper. This means it will react more with outside elements, this reaction can remove it from the metal and leave the less reactive copper behind. In terms of reactivity, zinc is a lot more reactive than copper which is why dezincification can be a serious problem with brass in the wrong conditions.
How to prevent dezincification
Some brass alloys can be more resistant to dezincification than others, they often have other elements added which are even more reactive than zinc making the brass more resistant to dezincification. Tin brass is one example of such an alloy. It has a tiny amount of tin added, around 1%, this, however, makes it much more resistant to dezincification than a standard brass alloy.
One way to help prevent dezincification is to clean your brass regularly and wear gloves when doing so. The acid on your skin can cause dezincification.
When brass ages and particularly if it is exposed to the elements it begins to tarnish. It will lose its shine, often darken in colour and appear patchy and blotchy. This is brass tarnish, but don’t worry there are lots of items that can clean tarnished brass and bring your brass back to a brilliant shine.
Cleaning Brass Tarnish
Now that you are aware of brass tarnishing you will naturally want to know how to clean it. So we have gathered together a few different solutions, some natural home remedies some purpose-made cleaners.
Issues with natural home-based cleaners
Many of the options often listed on cleaning sites and blogs often work because of a vinegar component. This can cause dezincification in brass if used regularly, so please use with caution. We would advise purchasing a purpose-made brass cleaner instead!
Apparently, ketchup makes a good brass cleaner! We put it through its paces on a piece of scrap brass we have which has tarnished. We will also compare it to white vinegar, another household solution which is apparently effective against brass tarnish.
Ignore the red in the above image, that is paint that was already on this scrap piece of brass.
Another brass item remedy. First, clean with soapy water and then apply some white vinegar to a cleaning cloth and get scrubbing! This method does require quite a bit of elbow grease so you have been warned.
As you can see from the images the vinegar worked a lot better than the ketchup. However, as we have already mentioned both of these methods can cause issues through dezincification of the brass alloy so we do not recommend them on valuables. We would recommend using a purpose-made brass cleaner like Brasso.