Today we are working on our 1/20.3 scale Chama coaling tower, making rusty steel corrugated roofing panels from aluminum craft foil. This system also works in “O” scale and perhaps smaller scales.
The process involves running 36 gauge aluminum “craft foil” through a paint tube squeezer, a device normally used for squeezing every drop of paint out of a tube of artist paints. Running the craft foil through it produces a great-looking 3-inch scale corrugated steel panel that can be used on a large scale (1/2″ to 1/20 scale) roof or siding, even a fence!
In smaller scales, it requires building a jig by perhaps soldering or gluing brass rods onto a brass plate or perhaps gluing plastic rods to a plastic base. The foil is then pressed onto the jig and burnished into form with a flexible tool, something like a stiff chisel-shaped pencil eraser. It may be possible to use a finer foil in the smaller scales, but boy would that be fragile! Keep in mind that cooking foil is also available in heavier and lighter gauges as well.
On to weathering! In this case, we are adding rust and rust damage with ferric chloride copper etchant solution, the stuff they use to etch circuit boards. It’s TOXIC! So we used it outdoors, with eye protection a smock, and rubber gloves. The panels were removed from the acid with tongs, in this case, tweezers. It was placed in a disposable plastic tray. A batch of “soda water” was also placed in a plastic tray. This too should be disposable as the acid will destroy it as well. And finally a large bowl of water. To rinse and hold finished panels. This bowl will not be damaged by the acid. (In theory)
The panels were placed in the acid bath to etch. Depending on the temperature of the acid this can go very fast! If the acid is room temperature it may take one to two minutes to get the reaction you want. Be sure to “agitate” the pannel with your tongs to break bubbles and speed the reaction. If the acid is even a bit warm it will “go off” in seconds. The reaction builds heat, so each panel will etch faster than the last. If you stay too long in the acid, you may dissolve the entire panel! One trick I used was to stand the panel in the acid after etching the entire panel, letting the end of the panel totally dissolve. Looks great! If what you are after is a totally rusted out panel.
The panel is then dunked in the soda water. This stops the reaction, but not instantly! The interaction between the acid and soda creates a new reaction, which seems to strip some of the surface aluminum which remains in the soda turning it to a gray paste over time. The soda also stains the panel dark gray, however, over time much of the gray color diminishes leaving the “rust” color from the iron in the ferric chloride. The soda also tends to cling to the panel leaving a texture that may be something you like. Or not. I removed it on most of the panels with a toothbrush. And boy did that brush taste nasty for a while! THAT’S A JOKE PEOPLE! DON’T DO THAT! Anyway leave some, remove some, mess with it!
After the panels are removed from the rinse water they are all dark grey but as they dry the red color comes out. Over the next hour or so they really change.
36 gauge aluminum Foil