A while ago, I received a cute gift from my partner. A europe scratch map. It features scratchable fields for a lot of european cities. The idea is to scratch them free, when we managed to visit it. Removal of the silver membrane would then reveal the same artwork that is printed in black on the membrane, in full color. It is a wonderful gift! It not only shows us and brings out memories of our trips on an almost daily basis, but it also gives inspiration to new ones!

Ideation and Basic Concept

Anyhow. When I received this gift I obviously needed a nice frame to put it up. But I did not want to always open a frame to reach the scratch map to scratch, anytime I am in need of scratching the scratch fields - who would want a scratch workflow like that?

So I thought I could build two nice looking poster-wide clamps that hold onto it and allow for some hanging mechanism. I still had some simple building wood around, roughly about 2cmx5cm out of pine. The idea is to cut equal parts and use those each as a jaw for the clamp and then use mounting hardware to fix the poster in place.

Building the Jaws

The build for the jaws is relatively straight forward and if it wasn't for the mounting hardware, I may have not even made a blog post about this anyway but first things first.

The basic design for the jaws is relatively simple. I simply rounded the top edge of each jaw into the full radius the was possible for the depth of the wood. In addition, I did not want the mounting hardware to pertrude out into the room or even worse in the back wall-facing to scratch the wall while hanging. So I drilled th clearing for nuts and washers on either side.

Then, putting on a coat of some oil that I had lying around and let it sit.

Blueing the Mounting Hardware

Now here we come to the interesting part. I did not want any shiny hardware on this build, as the poster shall be and remain the eye catcher. However, for the life of me, I did not find any black mounting hardware. So I decided to do it myself.

The only thing that I found was standard galvanized steel. So, my thought was, I could try and create blued steel from these parts. And there is a rather easy home brew method to achieve this. So I got to work. First order of business was stripping the galvanization. That can be easily done in a quick bath of hydrochloric acid:

Zn+2HCl→ZnCl2+H2↑

It starts to bubble quickly and dies down when the hardware starts to turn to matt gray from the shiny silver it started with. Then straining them with and rinsing them with a stainless steel strainer should remove and neutralize any remaining acid.

Now, with bare steel hardware I need to create a layer of magnetite, which is the black blueish oxidization step of iron. To create that, one can dip the steel into blueing liquid (which I don't have) or simply boil rusted steel. The issue is, that magnetite requires more energy to form, but is almost as stable as the red rust that already forms at any temperature. However, magnetite is much denser and adhesive so it has much better protective qualities as it can create a sealing layer arount the steel. That and it looks so much better obviously.

I needed to first create some layer of red rust, hematite, to turn it into magnetite. And I did not want to wait a week for it. So I tried a lot of remedies, oxidization agents to create rust fast. In the end, what did it was hydrogen peroxide. I few seconds bath inside that liquid and I had a full set of reddish hardware.

Now what needs to be done is creating an invironment of higher energy to convert this layer of hematite into the more appealing magnetite. And it turns out, not a lot of heat is required, as boiling it in water will already do the trick:

This process technically should be repeated a couple of times to get a fully sealed layer. But as my requirements were only of visual nature, I stopped at the second run. And I was quite impressed with the results:

Putting it all together

After finishing the hardware, I simply had to assemble the entire thing. The jaws were fitted with some hinges to put the together and then I added a strip of foam to give the jaws a little cushion when gripping the paper. For the attachment to the wall, I selected a simple hemp chord that threads through two holes on the top jaw.

Putting in the poster in between and bolting down the hardware create some clamping force that should keeop the poster in place. And here is the end result. I hope you enjoy.

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