Bright chrome looks good for a while, but one little dent and it starts lifting away, letting moisture reach the steel beneath. That’s why our fire truck bumpers are polished stainless steel. It takes more work but they keep their showroom shine for the life of the truck, which is more than you can say for chrome.
These polished stainless steel bumpers start life like any other metal fabrication: with precision cutting and bending. Then the real work begins. Study the surface of a just-fabricated bumper under a microscope and you’ll see faint scratches. They reflect light in all different directions, which is why it looks dull. Getting that surface to shine means polishing out those scratches until it’s mirror-smooth.
Now if you think about this you’ll realize we don’t actually polish out the scratches. What we do is remove the high points, lowering the surface of the stainless until it’s all the same level. That takes a cutting action, which we achieve with a combination of black sisal polishing wheel and black sisal compound.
Sisal is a coarse abrasive fiber made from the agave plant. (Yes, the same plant that gives us tequila.) The “black” is actually emery paste; basically crushed rubies, also known as aluminum oxide, and a grease binder. Together with the sisal it produces a cutting action that levels out the surface of the stainless.
We use two different machines for polishing, both of which were custom-made for the job. A semi-automatic polisher does the body of the bumper and a polish/lathe machine does the ends and corners. Both machines hold the sisal wheel while a skilled worker holds and moves the bumper against it until all the scratches are gone.
Then we have to buff the finish to get the final shine. Buffing is really just another polishing process, but one that’s softer and removes less metal. We buff with a yellow polish buffing wheel and a green polishing compound, again moving the bumper around against the wheel until we achieve a mirror finish. (Incidentally, we didn’t pick those colors because they look good: both are very specific materials that give exceptional results on stainless.)
So that’s how we get the mirror-like shine on our polished stainless steel bumpers. You could say it’s down to sisal and emery; we’d rather think of it as tequila and rubies.