I have virtually no experience with commercially made stains, so the approach outlined here
is probably not transferrable to "off-the-shelf" stains.
Before getting started, here's a helpful hint that can save you some effort...
Full Strength Acid Once you're ready to start putting acid to concrete...SQUIRT SOME DISH SOAP INTO THE ACID STAIN. This will cut the surface tension and allow for better penetration of the stain into the concrete.
- Full strength muratic acid is very corrosive and will quickly eat away cement paste if applied too liberally. When using the stains you make yourself using the approaches outlined here (both for copper and iron), I suggest watering them down.
- Take a small amount of the stain, which is dark and opaque (or should be) to begin with and add water until you achieve a light straw color (see the images to the right).
- The light color is deceptive. It is capable of producing a nice, deep brown color.
NOTE: After adding water to dilute the pH of the straight acid I sometimes will add some additional oxide...not much...just sprinkle a bit more into the mixture and stir some. Operating on the premise that the greater the concentration of metal atoms the deeper will be the color of the stain, adding enough until one obtains good saturation seems like a good approach. If you find some oxide not dissolving completely and subsequently collecting at the bottom of the container, not to worry, just recycle it for later use.
NOTE2: You could also drop in some old nails or rusty scale to the watered down solution.
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| Watered-down Acid Stain |
- Most everything I work on has vertical surfaces, so if you are wanting to stain a horizontal surface, my suggestion is...experiment, experiment, experiment on test pieces yourself to develop a feel for results before you commit to staining what you really want to work on.
- Using the watered-down acid solution, take an old brush and begin applying
it in relatively small amounts. I just barely dip the brush and repeatedly
go over the same area. I generally try to prevent "runners"...i.e. rivulets
of stain that roll down the side of the piece below the area I'm currently
applying stain to. Since "runners" are somewhat inevitable (acid is basically
just water after all), I at least "catch them", stroking upward toward the area
I'm working on.
Note that if one is partial, you might find the effect of "runners" appealing and simply let them go.
- The final two pictures shows a piece before and immediately after applying the iron-based acid stain made by adding one-eight cup black iron oxide to two cups of muratic acid.
- The piece is still wet in the final picture, but the final appearance wouldn't be much different if one applied an acrylic sealer at the end of the process. (NOTE: this piece was eventually used as the pedestal for a birdbath.)
- Even though color develops relatively quickly with iron stain, I leave it overnight as a general rule to allow whatever reaction is taking place to have plenty of time to run its course.
- The staining process leaves a slight residue which will need to be washed and scrubbed off.
- After cleaning the surface and allowing it to dry completely (usually another
day or so), its ready for sealer, which really brings the color out.
Before Stain 
After Stain
One final note: It's been my experience that good color development sometimes requires more than one application of stain. As a general rule, I will apply stain to fabric formed pieces at least twice, sometimes three times.