Why is mirror polish brass Better?

Welcome to Matt’s Metalworking, in this tutorial I will be showing you a beginner’s guide on how to polish brass with a mirror finish by hand. I’m just using a piece of raw brass, so you can see it’s quite rough and it’ll definitely be more work intensive than compared to a machined piece or something that is already finished just needing to be refinished.

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Required Tools

• bucket with water
• backing pad
• clean soft cloth

Required Materials

• 600 grit wet/dry sandpaper
• grit wet/dry sandpaper
• grit wet/dry sandpaper
• grit wet/dry sandpaper
• alloy polish

Depending on the surface’s damage, this will depend on what grit of sandpaper is required. For this I am starting out with 600 grit sandpaper, this needs to be a wet/dry compatible paper. The sandpaper needs to be pre-soaked before we start the sanding process. I have a bucket of water beside me, if you wish you can mix in soap to help with lubrication that can allow for a finer finish. For this tutorial, I’m just using straight water.

The heavier surface damage, the lower the grit is required. However when you go to a lower grit, this also means more material will be removed, and as you increase to a higher grit, slightly more work is required to remove those heavier grit scratches. When starting out with that first grit of sandpaper, most of those surface imperfections should be removed. This is basically the rough in step. Rinse off the surface to remove any access sanding material and always keep the sand paper well lubricated.

Moving up to grit wet/dry sandpaper. The reason I am wet sanding is so that the dust is kept down and we can achieve a finer finish. The black backing pad I have keeps even pressure on the surface with minimal distortion as what you may find when only using your fingers. For irregular shaped surfaces, you maybe able to use a foam backer instead.

For an addition example using an abrasive pad. Just like sandpaper, these too are available in various grits and is typically distinguishable by the color of pad. The maroon pad is listed at about 320 to 400 grit. These can be used with water as well which I am doing here. These pads are great for irregular shaped objects, but they don’t necessarily remove surface imperfections. Instead they smoothen or round off those imperfections. Sandpaper with a backer on the other hand can promote more of a smooth surface.

Moving up to a finer grit, this pad is green and rated at about 600 grit. Always keep the area well lubricated and rinse away excessive material. I’ll be stopping here to demonstrate what happens when you don’t use a fine enough grit before moving onto a polishing compound.

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This illustration helps explain the difference between using sandpaper and abrasive pads. Starting out with the existing surface and surface imperfections, each has high and low spot. With the sandpaper and a backing pad at the top, this removes all material evenly and also takes down the high spots from cratering marks. If you want those deeper marks to be completely gone, more surface material needs to be removed unfortunately. So this can result in more work, thinner surface, and changed dimensions.

Using abrasive pads, these may leave the surface uneven and won’t remove surface imperfections complexly. Instead it’ll round off those marks and cratering. Which methods you go with is really your personal preference and what type of shine you want to achieve.

Now moving onto the polishing stage. You can use a polishing compound such as what is used on automative paint or a metal or alloy specific polish. Here I am using an aluminum wheel polish.

I typically start out with soft paper towel first as metal polishing can make clothes quite dirty and hard to clean afterwards. Paper towel can be easily thrown away and we can finish with with a soft cloth at the end. Apply the polish to the cloth and work it into the surface. I will be polishing both the areas I used sandpaper and then the abrasive pads.

Work the polish into the surface, apply more polish when needed, and wipe away if the old polish gets too excessive. The polish will turn black which is perfectly normal as it’s removing a very light amount of material.

Once the surface is almost finished, finish up with a light amount of polish and a soft cloth.

And this is what we’re finally left with. You may see some mild scratching, therefore more polishing would be needed. There is still some surface imperfection, but they are much less than compared to what we started with. Finishing up with the 600 grit abrasive pad, while it’s still somewhat shiny, it doesn’t have the clarity than compared to using a finer grit. You can also see the existing raw finish before we started on other parts of the brass bar.

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To my eye, because the scratches look like they have a somewhat common orientation, it looks like either you have not completely removed the coarser scratches from some prior rougher grit stage during the progression. Or, sometimes if your polish applicator (cloth, paper towel, whatever) itself is somewhat abrasive, it can introduce new scratches during polishing. Or maybe you used the same polishing applicator/wheel/buff of the coarser grit on the finer grit?

A finishing technique I use is change direction with introduction of every new grit. Example, if you sanded radially with 600#, then switch to longitudinal on 800#, then radially again or completely different offset angle at #. You should only see uniform micro-striations of the finer grit with no underlying striations of the prior coarser grit. Vs. if you always do them in the same direction, then prior deeper scours which haven't been completely removed may be getting masked. This isn't always possible on all objects (especially round things where you are trying to keep dimensional conformance), but something to try & do if possible. Brass has nil porosity unless its a very weird alloy, so you should be able to get it to near mirror. Also some polishes have a wax or agent which is more like a thin gloss coating which enhances shine & tricks the eye a bit. As opposed to abrasive only polish. The wax/additive type makes the finish look better for sure, but the wax typically wears or evaporates over time. But that's a different issue.

I also know that photographing metal makes them look worse than in real life so you probably have a nice finish, just want it better.

I just finished a few pen kits & other Xmas objects myself for the first time. I was lurking on that IAP forum & got some good ideas. But I have discovered I do not like 'the brown stuff' on my metal lathe even with ways wrapped in Saran & vacuum on. So if I ever pursue this as a hobby I'd be on the lookout for something like a Taig or Sherline. A lot of guys use a wood lathes but typically not for mostly metal bodies. I don't really have the room or the desire for a separate lathe.

Lets see some more of your work, I'm interested! Thanks for all the advice, I will try Peter T's method of different directions for different grits and see if I can get a better finish. When I started out, I was making pens out of copper which finishes and polishes beautifully but is a cast-iron bitch to machine. I would have to stop and resharpen bits often, especially when drilling out the interior. Then I started using brass which machines beautifully but is harder to finish, and electroplating it with copper. That is how I will continue, if I can get the fine scratches out. Electroplating doesn't cover up the fine scratches, they show right up in the copper and by then it's too late to get rid of them.

These aren't in any particular order, just various ones that I've made .
This was the first pen I sold, probably should have gotten much better before I started selling them, but a friend overseas saw them on my Facebook and wanted to buy a few. She bought this one for herself and bought another one to give to J.K. Rowling as a birthday present (we all lived in Portugal at the same time), apparently buying presents for billionaires is a difficult thing!


Experimenting with different finishes, this was a thin layer of spray lacquer, but it didn't hold up to daily use. I want to get away from using Cyanoacrylate glue (superglue) which most pen makers use as a finish because a lot of makers develop sensitivities to the chemicals.


This is an electroplated pen, showing how the fine scratches from the brass show through into the copper.


Rejects get adapted into suncatchers and Christmas Tree ornaments.


A copper blank showing the difference between unfinished and on the way to being finished.


My first pen in copper for my wife. I hit it utterly out of the park on my first try and haven't come close to this again. This has a CA Finish which still holds up.


This is J.K. Rowling's pen.
My first two pens with CA finish. I've been using CA as an adhesive for models for +30 years but never considered as a coating system. But after seeing so many examples I just had to try out of morbid curiosity. I think there are better finishes but its the rapid buildup of glue + accelerator. Doing a regular clear coat would take much longer.

I went to polish on Green too soon. The picture looks better than real life. I can still see the rolling hilltops of the glue lines that were not blocked down to the base of valleys. But I kind of messed up the wood diameter which was already proud of the pen body diameter & was getting concerned my CA application was too thin in that area so I stopped. On brown burl I applied more coats & blocked with 600# between coats & that helped. More thickness to work with & a better surface to start sanding. The trouble with pens is if you want to sand in a different direction to the rotation axis (longitudinally), you risk making facets which is even worse. What I find works best is a foam rubber pad backing with the right amount of flex. And as mentioned above, fine grit scuff pads have a nice way of conforming to surfaces.





aluminum model rocker covers with 600# scuff pads/wheel. I actually wanted more of a matte finish, just enough to blend out the prior hand filing/sanding. Some people use the scuff pads wet with water or WD-40 id loading is an issue. I know it works on copper but the issue is almost immediate oxide layer, so there may be some tricks to specific polishes.

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I make pens in a Taig lathe, usually brass either left bright or electroplated copper. My question is about finishing and polishing brass. This is after 4 hours of using progressively finer grits of sandpaper, starting at 320 and ending at 12,000, followed by polishing with dialux yellow and blue. And I still have these fine lines. I want a mirror finish but at some point I wonder, are these lines just in the grain of the brass itself, or can I get rid of them? Any advice would be greatly appreciated!
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I have a LOT of experience polishing brass and other metals to a mirror finish by hand.

4 hours is frikken insane time to bury in trying to get a decent polish! Something is very wrong in your set-up! It's either a wrong choice in methods, or materials. Maybe both.

I would suggest among other items worth pursuing, for your needs, is a MicroMesh Kit. https://www.aircraftspruce.ca/catalog/cspages/micromeshstd.php These are used for polishing aircraft wind screens and making them optically 'near' perfect. I have found that going much past grit is a waste, on most metals, unless you are trying to produce a truly flat, perfect, mirror finish! (hint, use a very flat, solid ( I used a lot of Acrylic sheet offcuts, because I had them), backing block as you sand that mirror face!) Past grit or so, you can get a great, near perfect finish, with a clean, soft cotton cloth or a lint-free towel and some metal polish (look for Solvol Autosol! my recommendation!) Clean carefully with soapy water between grits, and wipe off carefully! Use clean soapy water to lubricate the sandpaper (a couple drops of dish soap in a 500 ml squirt bottle is good!) when sanding.

But you should be able to get a lot closer than you have, using autobody grades of sandpaper (up to - grit usually available) used wet, with a little dish soap in the water, as well as some clean soft cotton cloth and metal polish. Same rules apply! Clean between grits!

Primary effort needs to be put in to removing ALL of the previous grit's marks before moving on, and paying close attention to keep from contaminating higher grit abrasives with lower grit particles! At first, you will likely have to step back in the process to restart it at a lower grit, but if you can pay enough attention to a project to work on it for four hours and still not be happy, I figure you have it in ya to spend 35 or so minutes and pay close attention, and get great results! It's a bit Art, and a Bit Science, but these are my experiences in doing what you are trying to!

FWIW, I would work in the same linear direction through all the grit ranges. I found that I had far fewer artifacts of previous work, showing up on the finished product. I did a LOT of this work, by hand, rather than under power and spinning, which would have been MUCH quicker!

Per your later posts, I would say that your problem is one of cross contamination, rather than of a problem with the metal. Consider whether your polishing papers are embedding particles into the work, that are ruining the later efforts! Suggest light pressures, and LOTS of cleaning between wet passes, of the various grits. I know that I never had any trouble getting to a near optically perfect surface, at far less a grit than you claim to be going to!