Pigments vs dyes

[Mike Davis]

[h=1]Pigments vs dyes[/h]Pigments are coloured powders that do not dissolve in the liquid with which they are mixed. They have to be regularly mixed and ground in the (liquefied) binder. Properties of the paint such as colour, tinting strength, opacity/transparency and lightfastness are determined, among other things, by the type of pigment used.
If a colour-giving substance dissolves in a liquid (disintegrates such as sugar in water) we do not call the colour-giving substance a pigment but a dye.

a. Pigment - insoluble
b. Dye - soluble
[h=1]Dyes[/h]
[h=2]LIGHTFASTNESS AND APPLICATION[/h]The lightfastness of soluble dyes in paint or ink is poor to moderate. They are therefore not used in products for artists. A painting must be seen, and light is necessary for this; the colours must therefore be durable.
For the illustrator or hobby artist lightfastness is not so important. An illustration is printed, after which the original can be kept in a dark place; children and hobby artists do not have the same requirements as artists when it comes to the durability of colours. Due to their solubility dyes are highly suited for colouring thin liquids with a particular transparency, for example children's squash, as well as transparent inks.
Soluble dyes bleed; the colour penetrates other paint layers or spreads throughout the immediate area.
Royal Talens uses dyes only in two products: Ecoline (with the exception of white and gold) and waterproof drawing ink (with the exception of white and black). The lightfastness of these products is not indicated on their packaging. Works of art produced with soluble dyes can be best stored sealed. The above exceptions are pigmented, opaque and very lightfast.

 

[Mike Davis]

https://www.highlandwoodworking.com/woodnews/march_2006/alan_noel_march.html


https://www.popularwoodworking.com/...gment-or-dye-in-minwax-stains-does-it-matter/


http://www.howstuffcompares.com/doc/d/dye-stain-vs-pigment-stain.htm

 

[Mike Davis]

http://hingstssignpost.blogspot.com/2013/02/differences-between-stains-and-dyes.html


Dyes and stains are both used to color wood. To the uninitiated masses both types of products are one in the same. For this reason, these terms are frequently used interchangeably albeit incorrectly. While both dyes and stains are similar in appearance and intended use, the similarity ends there. In fact, dyes and stains each have their own distinct physical properties and resulting performance characteristics.



So how are dyes and stains different? The most salient difference is the colorant used in their formulations. Stains use pigments. These are very large, opaque, insoluble particles. What insoluble means is that you can mix a pigment in a solvent, such as oil or water. While the solvent will temporarily suspend the colorant in the mixture, the pigment will never dissolve. In time, these suspended particles will settle in one globular, muddy mass to the bottom of the can. This is why you need to stir a can of stain before every use to remix the pigment with the solvent. If there is no glob of pigment at the bottom of the can, it’s not really stain.

Is this a stain or dye? After one year on the self, no pigment had settled to the bottom of the can. The thin coating was also very transparent.

Dyes, on the other hand, are comprised of much smaller molecules. The molecules are so small, that light can pass through them unimpeded. While are insoluble, dye particles will dissolve in a particular solvent. If you buy dyes in powdered form, some are formulated to dissolve in alcohol, while others have been developed for water or a solvent such as turpentine, naphtha or lacquer thinner. Once the dye is dissolved in its solvent, it remains as a solution. Never should the particles settle at the bottom of the can.



The composition of stain is similar to that of paint. In fact, some describe stain as being very thin paint. Both paint and stain are comprised of pigment, a solvent and a resin or binder. Applied to wood, while both slightly penetrate the surface, stain and paint are primarily surface coatings.



By comparison, dyes are merely comprised of a colorant and a solvent (either alcohol, water or an oil-based solvent, such as turpentine, lacquer thinner, naptha or toluol). Unlike stain, which coats the surface, the tiny molecules of dye penetrate deeply into the fibers of the wood. Because of this deep penetration, dyes do not require a binder.



The choice of using either a stain or dye is in part subjective. Stains are a popular choice. But the opaque nature of pigments tends to obscure some of the beautiful graining of woods. Being transparent, much more of the wood grain and natural beauty are visible using a dye. With respect to durability, the larger molecules of the pigments used in stains are much more lightfast than dyes. Dyes are typically not very lightfast, including alcohol soluble aniline dyes and oil soluble aniline dyes. Water-based aniline dyes, however, have become popular because they provide improved UV resistance to indoor lighting. Under no circumstances, are any dyes recommended for exterior applications.



Test, Don’t Guess. Whichever you choose, before using either a stain or dye on a project, test the coating on a scrap piece of wood.



If you decide to use or experiment with dyes, you can buy these products in either powdered form or as a premixed liquid. Water-based products will provide better fade resistance than either oil-based or alcohol-based products. To mix the dye using a dry powder, approximately one ounce of powder is combined with a quart of warm water. You can, of course, vary the portions to achieve either a lighter or darker color. Or can create custom colors combining different dyes.



If you use water-based dyes, keep in mind, that these products will raise the grain of wood. The procedure is to first sand the wood, and then moisten the wood to raise the grain. After saturating a rag in distilled water, wring out the excess. Use the damp rag to wipe down the surface. Another method is to spray the surface of the wood with distilled water, using a spray bottle. Either method works. After the grain has raised and thoroughly dried, sand the wood 220-grit sandpaper. To ensure that the wood has dried completely, many woodworkers will wait overnight. You can accelerate drying by gently heating the surface with a heat gun on low to medium heat. After sanding, you can apply a water-based dye. In most cases, the water-based dye will not raise the grain again. Typically, the grain will only rise once.



Before applying the dye to the surface of the wood, spray the surface again with the spray bottle. Moistening the wood just before brushing or wiping on the dye, will prevent any blotchiness and produce a more even and aesthetically pleasing appearance.



Whichever type of dye you use, you will need to work fast to avoid lap marks. Using an alcohol-based dye, you will need to work especially fast, because alcohol dries like right now. Water-based dies are easier to work with, because they have a longer open time.



One useful technique when working with any of these dyes is that once applied to a surface, you can lighten the coloring by wiping the surface of the wood with a rag saturated with the solvent used in the dye.



Wiping technique when applying stains. Because the pigment in stain is opaque and tends to hide the wood grain, you can wipe it on and then before it dries, wipe it off. The colorant lodges itself in the open microscopic irregularities of the wood’s surface. Using the wiping technique, can bring out the dramatic contrast in the grain of the wood. While you will not achieve this contrast when dying wood, dyes produce deeper, more uniform color. This is especially true when working with a very hard wood.

My crucifix carving was dyed with an alcohol-based analine dye. After the dye had thoroughly dried, the carving was treated with several coats of tung oil. Read more about drying oils at Finishing with Tung Oil.

 

[Jeff]

Useful information, Mike.

To my knowledge Minwax stains are all pigment based and need to be stirred well to resuspend the insoluble pigment particles before use (the sticky glob on the bottom of the can).

On the other hand, dyes are soluble in water and alcohols giving clear solutions that require no stirring once mixed.

 

[Graywolf]

Very good info Mike.

 

[Barry W]

Mike, Excellent tutorial.

 

[Mike Davis]

Nah, just a collection of info spurred by a conversation this morning.

I find it interesting that there is a lot of incorrect ideas being tossed around so I tried to find accurate sources.

 

[Mike Davis]

To my knowledge Minwax stains are all pigment based and need to be stirred well to resuspend the insoluble pigment particles before use (the sticky glob on the bottom of the can).

FROM BOB FLEXNOR:

My experience with Minwax stains is that cherry contains only pigment. Golden oak and puritan pine contain only dye. All the rest I’ve tested contain both pigment and dye.
I have no idea why it’s this way. These stains were formulated many decades ago. I can’t imagine that anyone at Minwax today, after the number of times the company has been sold, knows why.

 

[Barry W]

I find it interesting that there is a lot of incorrect ideas being tossed around so I tried to find accurate sources.

Following my missteps in finishing a project a couple of months ago I have read Wood Finishing 101 by Bob Flexner which has some of the information you have provided. Thanks for your research.

Oops! I had not noticed you referenced this book in your post.

 

[Graywolf]

This was spurred by my misstatement of pigment instead of colorant in terms of dye and pigment. I do know the difference, however, I misused the terms and treated them interchangeably. Mike questioned me on it and did not have a ready answer, I stated I would have to reread some old materials, ten seconds in and dang it I was using the terms wrong. It wasn't a total lack of understanding, but it was incorrect.

What I ran up on in my reading was some of the interesting sources of dyes and colors. The lengths folks will go to get a particular color. At one time a certain shade of yellow dye was achieved by collecting urine from elephants. This activity was ended however, it was found to be inhuman to force a limited diet on the animals. This color is now produced from a synthetic source, as are a lot of dyes and pigments.

Back to the conversation, we were discussing adding different colorants to epoxy. I've even used artist oil pant in epoxy to give it color, in fact you can add almost anything to it to add color or fill, to fill cracks, knots, and a sundry of other things in wood.

Good info Mike!

 

[danmart77]

https://www.ncwoodworker.net/forums/showthread.php?t=65742&highlight=crealbilly

Mike this was discussed in another thread and the results were more confusing than the question.

I hesitate to add to the comments above but I would add the omission of some of the characteristics of metallic based dyes is worth revisiting.

 

[KenOfCary]

FROM BOB FLEXNOR:

My experience with Minwax stains is that cherry contains only pigment. Golden oak and puritan pine contain only dye. All the rest I’ve tested contain both pigment and dye.
I have no idea why it’s this way. These stains were formulated many decades ago. I can’t imagine that anyone at Minwax today, after the number of times the company has been sold, knows why.

That might explain why one of the few Minwax Stains I like is Golden Oak. It's really a dye.

And this discussion started on the Sunday Morning chat. Join us around 9AM every Sunday to start your own topic or just find out what others are interested in. We had a good discussion yesterday morning.

 

[Mike Davis]

Thanks Dan but that is actually a totally different conversation.

This is about the differences between dyes and stains or more accurately dyes vs. pigments, which I found are both used in stains.

Dyes are much finer and are soluble, pigments are more opaque by nature due to the larger size and are only suspended in solution (not dissolved).

Pigments will settle out and dyes will not.

Pigments are much more resistant to UV radiation and therefor fade less or in other words pigments will retain their color for a much longer time.
The difference is in some cases 10 to 20 times as long, so a dye may retain color for 5-10 years while a pigment may last 100 years.

Dyes are absorbed into wood fibers while pigments lie on top of the surface.

Dyes can give you a much smoother appearance and allow the grain to show while pigments can appear blotchy and obscure the grain.

So, there are trade offs on both and you have to decide where you are willing to compromise the most.

Or if you are willing to use either.

 

[sawman101]

Thank you for all the great information!