What type of dyes can be used to stain granite rock dust?

Name: Paul

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Message: The nice people at Dharma suggested I post on your forum, but my question is so odd that I’m not sure where to place it.

I am trying to stain a granite rock dust to change it from dull grey to black. I was successful in doing this with Rit Black Azabache dye that I purchased at a local grocery store. Based on that success, I ordered Procion dyes from Dharma and am surprised to see that after an overnight soak in a water slurry bath, then drying in an oven, the dye completely separated from the stone and did not change the color at all. Dharma suggests maybe trying iDye since the chemistry is different, but I wanted to ask you first if you had any thoughts or recommendations?

Hi Paul,

What an interesting question!

First I had to wonder what Rit "Azabache" dye is, a more evocative and interesting color name than any Rit black dye name I have seen before. Turns out it's merely a matter of bilingual package labeling. "Azabache" is Spanish for "Jet", and just another way to say "black".

Next, there's no obvious reason to me to chose dye, rather than pigment. Procion MX dye is a dye that reacts with cellulose, other carbohydrates, and proteins; this makes it able to bond to wood, for example, but there's nothing about it that has any particular attraction toward granite. Rit dye is all-purpose dye, containing a mixture of detergent, salt, direct dyes for use on both protein and cellulose fibers, and acid dyes for use on protein fibers.

Dharma's suggestion to maybe try iDye would work if the direct dye is what's working in the Rit dye mixture, since iDye is a direct dye. However, it might be the acid dye in the mixture, rather than the direct dye, that worked in your Rit dye. It's also possible that the fact that Rit dye is primarily composed of detergent and salt, with only a little dye, helped the dye to adhere to the granite. A fourth possibility is that the black Rit dye mixture just happens to contain a dye with some tendency to stain stone, a property which you might not find in other colors of the same brand of dye, since different colors in the same line of dye contain different dye molecules.

Granite (as you must know better than I do) contains quartz, mica, and feldspar. All three of these minerals are based on silicates. I doubt that a dye optimized for attaching to cellulose or protein is going to have much affinity for granite. My experience with Procion and other fiber reactive dyes are that they don't much stain anything other than protein or cellulose.

The dyes in Rit dye and in Procion dye are soluble in water. This means that they would work, physically, to color anything that contains water, such as, say, agar gel. Since granite does not contain water, there is no advantage to water solubility in choosing a way to color it after it is dry. A black pigment, which by definition is not soluble in water, would make just as much sense to me as something to mix with granite dust to color it. Pigments are powdered substances which are used as colorants in paint, or mixed with liquid plastic before making solid things out of it; since they are not water-soluble, they are not likely to wash out in water, which could be important at some point. They are highly suitable for mixing with a liquid substance that will act as glue after it dries, causing it to stick to whatever they have been applied to. The choice of binder for a pigment depends on what properties it has to have in the long run, anything from soy milk to lacquer to polyurethane to acrylic paint binder. Water-soluble food dyes are transformed into aluminum-based insoluble "lakes" for use when pigments are needed, rather than dyes.

Granite dyes currently used on some commercially-available countertops appear to be solvent dyes. Solvent dyes are, as their name implies, soluble in oily substances, rather than in water, and are therefore resistant to washing with water. They are useful for coloring epoxy resin, so they are suitable for use on resin-coated granite or for cultured stone products that contain resin. The drawback of dyed granite countertops, as opposed to undyed ones, is that the dye is present only in a thin layer on the surface, so that it is subject, over time, to wearing off.

Is there any molecular charge to the components of granite? Both cellulose-fiber and protein-fiber textiles are negatively charged, and so are direct dyes, acid dyes, and reactive dyes. Another class of dye, basic dyes, is positively charged (they are also called 'cationic dyes'), so the dyes in that class are more inclined to cling to textile fibers by virtue of their molecular charge. Basic dyes are known for their tendency to stain just about everything else that they touch, too. Procion dyes do not stain plastic buckets or porcelain sinks, but basic dyes tend to stain just about everything the are spilled on. I wonder what they would do with granite. I would guess that there is no charge in granite to make them cling, but I don't know. It is possible that there is some basic dye in the Rit black dye that helped it to stain your granite, but we cannot tell because Rit's choice of dyes is a trade secret. There is no information anywhere, that I can find, on what actual dyes may be included in any Rit dye color.

I am not sure where to advise you to look for the types of dyes I have mentioned here. Solvent dyes and pigments are harder to come by, at least in the small quantities used by artists and home hobbiests, than direct dyes, acid dyes, and reactive dyes, since the dyes in the latter groups are useful in crafts projects. Companies such as Standard Dyes will sell quantities as small as one pound per color; they may be willing to send small quantities of each of several dyes for you to use in testing. They have several different lines of solvent dyes. PRO Chemical & Dye, which like Dharma Trading Company sells both small and large packages of dyes to individuals, sells a carbon black pigment among their PROfab Color Concentrates. Dharma's Pigment Dyes are already mixed with a binder, which may or may not be suitable for your purposes.

Paula,
Thank you so much for taking the time to write this informative email! Yes, I think you are correct that it makes sense to test cationic dyes since the granite has a negative surface charge. This may explain, in part, why the Procion didn't work. It also suggests that Rit would contain at least some cationic since it's all purpose dye. Can you tell please me which brand(s) are cationic? It doesn't seem like many websites offer this information, but I may be looking in the wrong place.

I'm glad to learn that granite has a negative surface charge, so basic dyes might meet your needs. I doubt that many of the Rit all-purpose dyes contain basic dyes, but some dyes used as acid dyes are actually basic dyes. 

I know a few good places to buy basic dyes. The best one for small quantities is Aljo Mfg, in Manhatten. (Please tell them I sent you.) They sell them as "alcohol/water" dyes, because that is how these dyes are used for silk painting. They sell quantities as small as half an ounce per color. You will have to call them to order, because their website does not have online ordering. Ask whether they have one or several black basic dyes, since you will want to try all of them, if they have more than one.

Jacquard Products still sells basic dyes, in their online Bulk and Specialty Store, but their minimum order is one pound per color, which is a lot when you are just testing. Sometimes if you call and ask, a dye company will send a smaller sample.

Standard Dyes sells Permacryl Basic Dyes for Paper and Kayacryl Basic Dyes for Acrylic. It might be worth testing them, because at least some of them will be different dyes than from the other sources. Their minimum order size is one pound per dye color.

It's probable that all of the black basic dyes are actually mixtures of several colors. I don't have a single unmixed basic black dye in my chart of basic dyes. How satisfactory a given mixture will be depends on its use. You will need to do tests. If one mixture separates into navy blue, orange, and pink, try another to see if it does not separate out under your conditions.

For quite a lot more information on basic dyes, including safety cautions, please see my page, "About Basic Dyes". I would appreciate it if you will tell me how well the dyes you test work out for you.

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