Brassing?
Camera bodies used to be made of an alloy. Mostly brass. When the paint wore off, the brass became visible. That's where the term "brassing" comes from.
Today's bodies are made of zinc and other light weight alloys ... note, many are also inexpensive plastics. But they are not that golden brass color, they typically are a dull silver hue or an off-white shade in the case of plastics. Still called brassing.
I go to great lengths to make sure my gear stays in pristine condition. That means padded cases, bubble wrap, gentle handling. I do the same with woodworking tools ... well, maybe not to the length of padded cases, but I make sure they aren't handled roughly.
Brassing can also happen from gentle handling. Take a few shots and put your camera down for a few seconds, you might end up scuffing the bottom on cement or stone surface. Over time, that can cause light brassing on the bottom of the camera.
If you do a search on camera brassing, you will notice quite a few hits where owners try to cover that brassing. Many have tried permanent markers (like Sharpie). Permanent markers aren't designed for this and have a transparent quality that still minimally shows brassing, plus, the color is off.
If you are buying a used camera, watch out for this. There are unscrupulous sellers out there that will try to hide brassing to make a camera body appear "newer" or more gently used than actual. If you hold up the camera and view it in various angles, you can easily see the color shifting where light hits the body vs light hitting the marker paint. Sometimes it is the color hue, and sometimes it is the difference of reflection ... the "gloss" factor.
There are other techniques discussed by owners trying to hide brassing. Those include those small bottles of paint used for hobby kits. It's usually a small brush built into the cap. Color choices can be considerable with some colors being close enough to the camera color. Again, it's all about gloss ... but in the case of these hobby kit colors, it's also about brush strokes. If buying a used camera, look for uneven surface.
Sounds strange doesn't it? An article on how to detect camera gear manipulation ...
We aren't in a perfect world where you can trust what sellers tell us. Let me give you an example. A few years back, I was looking for a replacement cell phone. The cell phone I had was a bit older and had a loose button that fell off. I replace it, but wanted a bit more reliability. I also thought I could get a better phone camera for impromptu shots. I must point out that I never get a phone that is built into a cell phone plan. If you looked closely at the cost of those cell phones over time, you'd realize just how close to illegal the interest rates are. I prefer to buy one year old and buy outright.
I did find a used one year old phone I was interested in. With a 102 megapixel camera, it was ideal. The price was a bit more than I was used to paying for used cell phones. I had already done some research and discovered that used cell phone scams were rampant. There were a few techniques suggested that helped a buyer identify scam phones and I noted each one.
I made arrangements to meet a seller in a public location (a local coffee shop). I had already clarified that I wanted to insert my own SIM card in the phone to verify that it would work on my provider's network (that helps to clarify if the phone is locked or still under a contracted plan). While the seller had initially agreed, he balked when it came time to actually do that. He thought I should take his word for it. He presented professionally. Dressed in a suit, story was credible ... the phone was his wife's and he was upgrading it as a gift to the most current technology (just one year newer, by the way). My reaction was quick. Sorry, but we agreed to try this with my SIM card ... no test, not buying, period. He relented. When I inserted the SIM card, it took longer than usual for the SIM card to be recognized. The information on screen wasn't quite right, at least not quite what I expected. Still not sure, I decided to run one more test. At 102 megapixel, that particular phone would be using almost all of the lenses on the back of the camera. It had five lenses, 102 megapixel would use three of them. If you fire up the camera app, and run your finger across the lens path (and about one inch away), you should see the "shadow" of your finger pass each lens in order. Nope, only interrupted one single lens, meaning two of those lenses were not active. A sure sign of a scam. I removed my SIM and pointed out the phone test ... and pointed out this was not a legitimate phone. Seller grabbed all of his stuff and ran out of the camera shop. I kept my money. His vehicle was not visible or I would have taken the license plate and called the police ... he ran off to the side somewhere (and I wasn't chasing).
The same thing happens with camera bodies and lenses. A camera body at least has a shutter actuation count that can't be hacked. But what about lenses? No shutter count and there is no way to tell how used (or abused) the lens is. What can you do?
There are two techniques, depending on the type of lens.
If it is a prime lens, looking at the front glass and rear glass is paramount. Bring a lens cleaning cloth and use it to make sure the glass is free of scratches and smudges. Check out the filter threads to make sure they are not damaged or broken. And check out the body of the lens to check for scratches, dents, and cracked or missing clear plastic covers (such as over the distance scale). Bring a flashlight so that you can shine it though the front (where you can see the inside of the bottom of the lens) and shine it through the rear (where you can see the inside of the front of the lens) ... you are looking for an undue amount of dust. On a prime lens, there is one moving part: the focus ring. Even when the camera is set to auto-focus, the focus ring on the lens moves. With movement comes the opportunity for air and fine dust to infiltrate the lens.
A zoom lens involves a lot more effort. Here's why. A prime lens only has a focus ring that moves – and that may not be that frequent or extreme. On a zoom lens, you have two moving rings: the focus ring and the zoom ring. Both are opportunities for find dust to infiltrate the lens.
Keep in mind that all used lenses will have some light fine dust inside the lens. These typically don't affect image quality and will not appear on the photo – unless it gets to be excessive dust.
There's also a problem with some lenses that are not stored properly. That is fungus. Unless the fungus is considerable, it is very difficult to see. That's where the flashlight helps. Fungus is not discriminatory ... it's throughout the lens. If it's there, you can see it on the back glass or the front glass. Shine that flashlight and look for a really fine (and tiny) wavy line. It almost looks like a tiny eyelash. Fungus can also appear like a fine star burst. If you find any fungus, walk away. There is no price point where a lens with fungus is worth buying. First, the fungus will only get worse – there is nothing from the outside of the lens that you can do to control the fungus. Second, there is no safe way to tear down a lens and "clean" the fungus. You have to remember that lens glass include some really fine multi-layer coatings and any fluid that can clean the fungus will also remove the coatings and render the lens useless.
Used camera gear can save you a lot of money. Some points to remember is that warranties for used camera gear is NOT transferrable. Warranties only extend to the original buyer and with proof of purchase. Don't believe me? Check out the wording on the warranties ... there isn't one single camera gear manufacturer (body or lens) that has transferrable warranties. If you are buying used, you are also accepting that risk. You might be buying someone else's problems. Here's an example ... I've owned three different Nikon 28-300 lenses. The first two zoom rings weren't quite as smooth as I would have liked them, so I sold them and kept looking (and note, that I told the buyers why I was selling and gave them the opportunity to try and test). Other sellers may not disclose like I do. Auto focus motors may be too noisy, focus rings (or zoom rings) may be too tight. Put your buyer defences up.