Acid Stain Using Iron

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If you make either of the following acid stain recipes, make sure you exercise proper precautions: Use goggles and rubber gloves and perform the operation outside or somewhere an acid spill would be relatively inconsequential if things go horribly awry. In short, always be careful.

Fast Method for Concrete Acid Stain Using Iron

Iron results in a nice earth-tone color.

1. Obtain some muratic acid (any hardware store should have it).
2. Obtain some BLACK iron oxide...check with your local ceramic supply. Iron oxides are frequently used as a component in glaze formulas. It is generally inexpensive (around a couple $'s/lb), so this is a great way to make some cheap stain.
   Note that you can buy yellow, red, and black iron oxides...so let me stress, be sure to get the BLACK oxide, even if the others are cheaper. My experience is that red and yellow don't react well with acid. If instant gratification is what you're after....get black iron oxide.
   Finally, note also that red, yellow and black iron oxides form the basis of virtually all earth-toned, integral concrete pigments, so if you also want to experiment with colored concrete, your trip to the neighborhood ceramic supply company would be a good time to stock up, although you can also buy integral pigments for concrete at hardware stores.
3. Sprinkle about one-eight-cup of the iron oxide into about two cups of acid. The reaction between the acid and oxide is not nearly as exothermic as the copper-oxide-acid reaction, but I think you'll find the container warm up as you add the oxide.

4. 

   Acid & Black Iron Oxide

   The photo to the right shows the result of adding about one-eight-cup of black iron oxide to about two cups of muratic acid. It is ready to use in only a few minutes.

NOTE: Always be sure to keep the container covered when storing...acid fumes will badly corrode any exposed metal nearby.

Slow Method for Concrete Acid Stain Using Iron

1. Obtain some muratic acid (any hardware store should have it).
2. Here are some possible options for getting some free iron to make your acid stain:
   • Old rusty stove pipe: If you can get ahold of some old, rusty stove pipe, the kind scale falls off when you bang it with a hammer, this is great way to get some iron to plop in your acid. It works really well. I actually prefer this over the fast approach using black iron oxide. This approach works reasonably quickly too...you'll probably have some usable stain in less than a week.
   • Old rusty nails: This approach works, but could take several weeks. I've used it successfully but it can strain one's patience, especially if you anxious to get the ball rolling.
   • Old mufflers/tail pipes: I've never used this approach, but if you can get some old rusty tail pipe or an old muffler that has been trashed by rusting out, this might work. If you try this and it works, please let me know...

     

     Rusty scale from old pipes.
3. Drop the iron into the acid. The question of how much rusty iron to add to the acid is a good question. I don't have a definitive answer. My general approach is to drop a "handful" of nails/rusty scale into several cups of acid. This seems to work.
4. There will be some bubbling and fizzing as the materials react, so if you drop the iron directly into a gallon container, don't screw the lid back on tightly.
5. Once the acid has taken on a deep, dark rust color, you will have some usable stain. You can even get usable stain before you get a dark opaque color. You just need to test a small amount of acid every couple of days. It will likely take at least a couple of weeks for this approach to yield a usable stain. I don't use this approach to making iron stain very often, so I've not experimented with it enough to develop a reliable feel for outcomes. But you should acquire a usable stain on a much quicker time scale than when taking the slow approach to making a copper-base stain.

NOTE: Always be sure to keep the container covered...acid fumes will badly corrode any exposed metal nearby.