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Homemade Brass Keychain
Description of the making of a brass keychain with the etching method. On the keychain there is the name of the owner and a QR code
During the last months I had different keychains, but none was good enough to withstand even a pretty light use, so I decided to replace my current one with a new one, using a custom design suited to year 2012.
The exemplar I am going to show in this article has to be considered a sort of (working) prototype, since it has different rough edges that a second exemplar would not have anymore.
The design was inspired by two other keychains, one of which I used in the past, and was adapted to the available tools and materials: it is a keychain made of chemically etched brass with four holes, with my name on the front side and a QR code on the back side. Two of the holes can be used to add removables groups of keys, for example the car or bike keys, since detaching them while driving is useful to avoid tinkling.
The QR code can be useful in case of loss: it contains my current email address and mobile telephone number: nowadays many people (and hopefully police officers as well) know that QR codes are 2D barcodes with data on them and most smartphones can read such codes.
The base material is a 75x38 mm plate of brass about 1 mm thick. On the front face I decided to write my name and I used Tex Gyre Chorus as font, being it a serif font but light serifs, easy enough to reproduce on metal with homemade etching and light enough on the eye. The test was printed on paper using a laser printer and then the actual text was cut out of paper with a sharp cutter. The result can be seen on the first picture.
The picture shows also some tape applied to the back of the plate, since I planned to etch only one side and to produce the QR code with different tools. The next picture shows the paper glued to the metal (previously cleaned with dish soap to remove finger oils). The small "A" written in the center of the "a" character was used to ensure the correct orientation of the paper insert.
I used normal liquid glue, suited to metal, paper, leather, plastic. It offered slow enough drying times (cyanoacrylate and hot glue are too fast drying) and also able to permeate paper, thus shielding the metal better from the external etching solution.
After drying some glue was spreading on the metal out of the paper, so I simply cut the excess glue with a cutter.
Concerning the QR code, the generation was performed on the http://goqr.me website, using the least amount of text to keep the elements as big as possible. The error correction data was increased to 15% since it did not cause a change in QR code size. Initially I planned to drill small 0.8 mm holes on the metal plate (to be later filled with paint) where a dark spot was required, but I had no suited drill bits so I decided to go for the etching method as well.
I printed the code on paper as well, then I glued it to the metal plate, previously covered with tape to protect it from etching. This turned out to be a mistake, since it complicated the removal of the black spots.
The removal of the main markers was performed by following the contours, while the removal of the single elements of the code was performed by cutting a uniform grid with the cutter to isolate the single elements and by removing completely only the black ones.
The tape on the back turned out as a mistake, because it made much more difficult to cut the grid through it down to the metal, it made difficult to remove a single spot without affecting the other ones around and also made the remaining single elements much more instable and prone to detachment. The result was the loss of some of them both during cutting and during etching. I replaced the ones lost during cutting with spots of permanent marker, usually oil based and therefore able to isolate the metal from the etching agent.
The etching of brass (copper plus zinc) was performed with some old HCl+H2O2 solution I had since last etching of an electronic circuit (60 ml of HCl 32%, 20 ml of H2O2 30%, 130 ml distilled water, for details see here), meaning the solution already contained some copper and the H2O2 was gone. I added some fresh H2O2 to freshen the solution (as results changed color from dark green to light green) and I was ready.
After at least half an hour and a couple of corroded stains on the steel kitchen sink I recovered the plate. The etching had been able to cut effectively the metal and the depth could be felt easily with the fingers.
I left the name as it was, but I painted the black spots of the QR code with a permanent marker, to increase the contrast and ease the recognition. The rough surface left by the etching and the etching depth ensure that the paint is stable and that it won't get scratched away easily. If the brass will turn very dark due to oxidation, it will stil be possible to clear it by rubbing rough paper on it and the marks will stay anyway.
Since the plate had been corroded also outside the expected areas, I polished the surface with a Dremel tool and I removed the visible copper areas. I also drilled the four holes (one unfortunately is partly damaged) and I thinned the border for two of them, where the removable bits will be connected as soon as I make them.
The resulting keychain is not as polished and regular as a commercial one is, but is already more than enough for the everyday use. As soon as the email address or telephone number change I will make another one, but I will try the toner transfer technique I already use for electronic circuits, at least for the QR code: It would speed up the process and it would coat directly the metal, without need of glue or paper. I did not use that method for this prototype because I thought that transferring large prints would have been difficult. Given the results with this prototype, the method is still worth trying.
I thank Florian A., Timo L. and Wolfgang K. for the help with the lab work and/or for the ideas.
Update: 2014-07-27
The ink of the black permanent marker fades easily due to friction with other objects in the pocket or with cloth, so I decided to clean it throughly with dish soap, then acetone, and to apply dark nail polish on the bare metal. It should stick and last much longer.
Author: Olaf Marzocchi
First revision: 2012-10-20.
Last revision: 2014-07-27.