Introduction: Black Bean Blue Stain

About: I am a Maker and Artist who experiments with a variety of mediums and projects. I also try to repurpose and repair as much as I can. Check out my instagram page @mitzsea_makes.

Blue ranks high on my list of favourite colours, when I learned that black beans can make blue I knew I had to try it.

I chose to stain my beech wood trestle desk legs and then finished them off with a clear latex (water based) topcoat.


  • Black beans (from the Latin section of the grocery, it makes a difference, more info below.)
  • Water
  • Calcium Chloride a.k.a. Pickle Crips Granules
  • Large pot or bowl
  • Paint brush
  • Water based clear coat

Step 1: The Beans

To get the pigment from the beans is really quite simple. Get a large bowl or pot and put the beans in. Then fill up with water about an inch or so above the beans. Then just let them soak. Stir the beans every now and then to release the pigment from the beans.

Though, there are some tips to have the best results:

1. The first soak of beans will give you the darkest pigment. So be mindful of how big your project is and how much stain you will need. That will impact how many bags of beans you use.

2. The second soak will yield a weaker purpleish-brown that can work but not as dark.

3. If you want to get the pigment out a little faster, I found that gentle heat on the stove releases it.

4. My project required 10 cups or 2500 mL of the dye. This should help give you an idea of how much you may need for your project.

Step 2: Adding the Mordant

I took the time to figure out which type of mordant would yield the blue I wanted for my desk. I chose to use calcium chloride because it gave the result I was looking for.

I used a 1:1 ratio of mordant to dye. My project needed 10 cups (2500 mL) of dye to 10 tbs (142 g) of calcium chloride.

When mixing the calcium chloride in the dye I gently heat the dye to make certain that the mordant is completely dissolved. There is no need to bring it to a boil or create steam, just enough to make certain everything is dissolved.

The fun part is that while adding the mordant you can see the chemical reaction occur. The blue just becomes more brilliant as seen in the second photo.

Safety notes: While calcium chloride is used for making pickles (canning food) it puts in the realm of a safer chemical, it still requires smart handling. Such as, keep out of reach of pets and children. Don’t get it in your eyes, etc.

Step 3: The Staining Process

In the first picture is the raw beech wood before I put on the first layer of stain. The subsequent photos show the progression in the depth of the colour, until the last photo of the completed project.

Staining the wood is a simple process, just get a natural bristle paint brush and start slopping it on. I apply the mixture until the wood has that wet sheen to it. I let the sheen dry up before I apply the next layer. The wood doesn’t have to be completely dry just not shiny.

Keep applying until you reach the desired depth of colour. For my project, it took about 6 applications for each trestle to get it as dark as it is.

Step 4: Tips and Discoveries

During the process of teaching myself about making this stain (dye) I discovered a few things that you should know so your project is a success.

1. There is a difference in the colour you get from varieties of black beans. The two varieties I tried are what I am terming Latin Variety and Asian Variety.

A. The Latin Variety is what I used to stain my desk. You can see the colour in the first picture. Once oxidised it turns from that purplish colour to that beautiful blue. This is the common variety you find in every grocery store.

B. The Asian Variety can be seen in the second picture. It has an inky-blue colour but once it oxidises on the wood it turns very purple. These are the variety you can buy from your local Asian grocery.

C. Even though I used the same mordant (calcium chloride) in both bean dyes, they yielded different colours.

2. Different types of wood could change the hue of the dye.

A. All woods are going to have their own pH and chemistry which could effect the hue of the dye. It is a good idea to test your dye on a piece of wood of the same type as your project.

B. Oxidisation is a big part of the process. Though the dye may look different in the pot it will change during the drying process to that nice blue.

C. Once the unused portion of the dye turns brown in the jar, it no longer stains blue. So you need to use it right away. It doesn’t even store in the fridge.

3. Be accepting of the variations that natural stains or dyes produce.

A. This is part of the fun.

4. You can find calcium chloride in the canning sections of your grocery store.

5. Use a water based clear coating for the topcoat on your project.

A. Use your favourite if you have one.

B. A clear wax works really well with natural stains.

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