Homemade Concrete Stain

How To Stain Concrete with Copper and Chromium

The blue and blue-green copper colors were nice enough, but I wanted to see if I could create the black color of cupric oxide or the red and yellow colors of cuprous oxide. Those oxides are not water soluble, but I thought maybe a soluble copper salt could soak into the floor and it could react with an oxidizer once it was already absorbed by the concrete.

This is a bag of bright orange Potassium Dichromate oxidizer from the pottery store. It looks pretty but it causes cancer so be careful.
day-glo orange colored powder

Ingredients

Technique

I stirred the Dichromate into the water but it was pretty slow to dissolve so I put it in a "Corning Visions" pot and warmed it on the stove over low heat to help it dissolve. I removed the dark orange solution from the heat and added 1 teaspoon of muriatic acid (HCl 31%) Why? I think I remember reading somewhere years ago about how Dichromate oxidation was somehow different in acidic solutions. So I guess the real answer is that it seemed like a good idea at the time. In any event it wasn't enough acid to cause fizzing when the solution was brushed onto the floor.

Anyway, so I added the Copper Sulfate and Sodium chloride to the hot orange solution and stirred to dissolve the sulfate. The solution now appeared to be almost black but when I held it in front of a bright light I could see it was actually dark green.
backlit solution appears green

I brushed it out over 10 square feet of concrete. The color of the freshly applied wet stain is dark yellow. This was too much liquid to be quickly absorbed so it formed little pools on the surface.
brushing solution onto floor

Orangey-red spots begin to appear as the stain dries.
burnt orange spots on wet greenish yellow floor

The longer it sits, the more orange it becomes. The only portions that have not changed color are those covered by little pools of excess liquid. So maybe the oxygen in the air plays a part in this chemical reaction or perhaps the liquid inhibits it in some other manner.
orange floor with greenish yellow puddles

Results

I wiped up the excess crusty stuff after the floor was totally dry. I decided to wear gloves while cleaning it up on the assumption that it was probably still poisonous.

This is how it appeared after cleaning up the excess and allowing it to dry out a second time.
orange floor except tan where stain puddles had been

Upon returning from two weeks out of town, I discovered that rainwater had leaked in under the sliding-glass door during a storm. The copper-based colors were altered by the rainwater but the iron-based stains were unchanged. The color of the area under the rainwater puddle was now brown but the portion of the floor that remained dry was still orange.
floor much darker two weeks later

Six months later, almost all of the orange had changed to a very dark brown color, even the area that was not exposed to rainwater. The white spots are morter that was splattered from a different project.
mostly dark brown with yellow and orange highlights

The same area looked much darker when it is wet. The floor appeared a vivid orange color the day the homemade stain was applied:
wet orange floor except bright yellow where stain puddles had been

Two weeks later after the rain leaked on the floor:
wet floor much darker two weeks later

Six months later the color ranges from bright yellow to dark coffee with a few orange highlights to make it interesting:
wet mostly dark brown with yellow and orange highlights

So I guess this experiment worked. This recipe produced some interesting colors, especially when the floor is wet. I'm not sure if these colors are due to the presence of Cuprous Oxide or Cupric Chromate... or both. Also I'm not sure that the color is so much better than the Iron stains an to justify the use of poison ingredients.

Another Try - Less Dichromate

I decided to try again using less Potassium Dichromate. The only change from the recipe above is that I used one Teaspoon of chromate instead of one Tablespoon. The solution appeared to be a very dark "peridot green" color, not black as before. I brushed the solution out over 10 square feet but this time the freshly applied wet stain was green, not yellow as before.
wet green floor

This test patch of concrete was not particularly flat so excess solution formed several pools. After waiting for 3 hours, I got impatient and spread it out so it would dry faster. I don't know if that changed how it would have looked but I thought I would mention it. Once it finally dried it looked very similar to the first attempt above:
orange floor with yellow tones

Results - Less Dichromate

I was bummed that it looked almost the same as the first attempt until I washed away the excess that did not soak into the concrete. Once the orange powder was removed, an interesting green color was revealed. This was more of a forest green than the blue-green color created by Copper Chloride. Perhaps there is some Chrome (II) Oxide involved?
green floor with orange and brown highlights

The same rainwater that altered the copper/chromate experimental recipe above caused a slightly different change to the area of the floor stained with the reduced chromate recipe. The area that remained dry was much more orange and less green than the area that had been wet. In fact, the green area seemed even more green than it had two weeks before.
dry floor two weeks later

Unlike the first, more concentrated recipe, the color of the floor stained by the reduced chromate formula did not change much after six months. The rusty orange areas became slightly more brown but the green colors were relatively stable.
dry floor six months later

As with the others, the color is more intense when it is wet. This photo was take the same the floor was stained:
wet floor stained with reduced chromate formula

Two weeks later after the rain leaked in:
wet stained floor two weeks later

Six months later there is no significant change in the green but the highlights are not as orange:
wet stained floor six months later

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