One of the most common questions I get asked about a Do It Yourself or professional leather furniture restoration project is: Will the color rub off on my clothes?
It’s a worthy question because there are certain types of coloring agents that will transfer, and others that won’t.
The short answer is that leather dyes transfer, and leather pigments don’t.
Apply a true leather dye (metal complex or aniline dye) to the surface of leather, and dye transfer will occur. The next time someone sits on the leather they’ll be wearing the dye on their clothing.
Whereas apply a pigmented coloring system and there will be no threat of color transfer.
Dyes
The reason is that dyes are free floating, tiny molecules that migrate. They are not made color fast. The dye cannot be “locked” in place if its simply applied to the surface. With a newly tanned hide, the leather can be processed at a tannery such that there is a minimal potential for dye transfer. This is accomplished through heat. The hides are typically dipped into vats of heated dye. The heat sets the dye to the best possible degree. However, take a damp, white cotton cloth and rub it across tannery processed dyed leather and you’ll pull some of the color. In an after market application of dye, you can't stick a leather sofa into a vat of heated dye. So you can't set the dye. The dye will transfer, and quite easily.
One consumer called me in a panic. She purchased Fiebing's leather dye (green) and applied it to her leather sofa. Two weeks later a little girl spilled juice on the sofa. The juice ran off the sofa on to the carpet, carrying the green dye with it. So, not only was the sofa ruined, but so was the carpet.
Pigments
Pigments on the other hand are carried in a specialized chemistry called a “binder” that locks the pigment molecule in place. Most binders are a resin blend of urethanes and acrylics. The combination of pigment and binder is often referred to as a "leather finish." This coloring chemistry renders a topical film on the leather with appropriate adhesion and cohesion properties and when fully cured does not allow color migration or transfer. The key is using a specific type urethane and acrylic chemistry and then getting the blend ratios correct. So if you are going to mix your own coloring system, you should have a solid understanding of chemistry. Use the wrong binders and the color coating will crack and peel.
If a leather technician says he will “re-dye” your leather, he/she probably doesn’t know the difference between a dye and a pigment. If he/she is really using dyes as a coloring agent, then expect the color to rub off. In most cases, the tech is actually using a pigment based coloring system and is referring to it as a dye.
There are two additional Blog entries that offer greater detail explaining the difference between dyes and pigments. They are entitled “Leather Furniture – Dyes or Pigments” and “Leather Color and Attributes.”
Of course you can learn more at our web-site http://www.advleather.com or http://www.DIYLeatherSolutions.com. You can also call our tech line to get more information about Advanced Leather Solutions, or if you simply have a question, we’ll gladly respond. We can be reached during normal business hours in the US at 510-786-6059. For time zone calculations, we’re located in California.
Copyright 2009, Kevin Gillan
Showing posts with label leather paint. Show all posts
Showing posts with label leather paint. Show all posts
Wednesday, June 24, 2009
Monday, March 16, 2009
Leather Colors and Attributes
The phone rings and answered: “Advanced Leather Solutions, how can I help you?”
A common opening response is: “I have a problem. It seems the color of my leather sofa is disappearing. What’s going on and can it be corrected?”
After a few qualifying questions, a conclusion is reached. The leather is suffering from print coat failure.
To understand what that means requires some background knowledge. Most upholstery leather is vat dyed (aniline) and then a pigmented coating is applied to the surface (more on the difference between dyes and pigments in another post). The topical color presented comes from a cocktail of pigment molecules mixed to create a specific rendering (i.e. brown). The pigments are blended in a resin-based chemistry called a “binder.” The result is referred to as the colored “finish.” All of this is then sealed with a clear coat which is the primary protection.
Now, here’s the meat of the matter. The binder and clear coat are chemically engineered with several important attributes:
1. Elasticity -- they have to flex and move as the leather flexes and stretches when sat upon else they will crack.
2. Cohesion – they have to establish a durable, wear-resistant film where each molecule links or “sticks” to its adjacent molecule else the will wear quickly away.
3. Adhesion – they have to adhere permanently to the surface else they will peel up.
4. Chemical Resistance – they should withstand the rigors of an active household else will wash away, sometimes simply with water.
5. Low Profile – they should follow the topographic contour of the leather flowing down the side, across the valley floor and up the other side of the grain pattern on the hide else they will bridge over the grain pattern, obliterating it.
Without these attributes the finish will come off, peel up, crack, appear like plastic (vinyl), etc.
Base and Print
To address the issue above, there is one other variable to consider. To present a color that looks natural a layered coloring technique is used. This is called a “base and print.” The base coat (lighter color) uniformly covers all leather surfaces. The print coat (darker color) is then erratically applied without complete coverage creating a mottled coloring affect. The technique gives the illusion of color depth, or a more natural look, resembling how a dye would render in leather.
It the case of the common question mentioned above, the tannery failed with at least two attributes: 1. Adhesion, 2. Chemical Resistance. The clear coat has eroded away and the print coat has been either worn or chemically removed (sometimes with simply water), exposing the base coat. Thus print coat failure ensues exhibiting as lighter color (the base coat) in the problem area. Often the problem is described as fading.
This is a correctable condition. It requires application of the missing print coat and then top-coating with a more durable chemistry so as to avoid the same problem from reoccurring.
As professional leather restoration and repair technicians, we see common threads of weakness in leather furniture. Typically there is a failure at some level in the basic chemical composition of the finish applied at the tannery. With an understanding of the fundamentals, we can generally develop a fix that solves the problem. However, it’s important that the “fix” itself not be problematic.
Here’s the rub. There are people representing themselves as leather repair technicians who have no clue about the fundamentals and cannot distinguish the difference between quality finishes and terrible finishes.
For example, many technicians will use colored finishes that have been engineered for vinyl or plastic. Leather is a very different material as it’s organic, not synthetic. This differential is important. Vinyl colors when applied to leather often crack and peel over time. So, it’s vital to determine if the color chemistry the technician is using is specific to leather. If the technician represents that he/she uses the same color chemistry for both vinyl and leather, then that is a prescription for failure.
To learn more about leather finishes, go to http://www.advleather.com/. Click on the leather care button. There you’ll find a description of the various types of leather and their finishes. You can also call our technical staff at 510-786-6059.
Copyright 2009 Kevin Gillan
A common opening response is: “I have a problem. It seems the color of my leather sofa is disappearing. What’s going on and can it be corrected?”
After a few qualifying questions, a conclusion is reached. The leather is suffering from print coat failure.
To understand what that means requires some background knowledge. Most upholstery leather is vat dyed (aniline) and then a pigmented coating is applied to the surface (more on the difference between dyes and pigments in another post). The topical color presented comes from a cocktail of pigment molecules mixed to create a specific rendering (i.e. brown). The pigments are blended in a resin-based chemistry called a “binder.” The result is referred to as the colored “finish.” All of this is then sealed with a clear coat which is the primary protection.
Now, here’s the meat of the matter. The binder and clear coat are chemically engineered with several important attributes:
1. Elasticity -- they have to flex and move as the leather flexes and stretches when sat upon else they will crack.
2. Cohesion – they have to establish a durable, wear-resistant film where each molecule links or “sticks” to its adjacent molecule else the will wear quickly away.
3. Adhesion – they have to adhere permanently to the surface else they will peel up.
4. Chemical Resistance – they should withstand the rigors of an active household else will wash away, sometimes simply with water.
5. Low Profile – they should follow the topographic contour of the leather flowing down the side, across the valley floor and up the other side of the grain pattern on the hide else they will bridge over the grain pattern, obliterating it.
Without these attributes the finish will come off, peel up, crack, appear like plastic (vinyl), etc.
Base and Print
To address the issue above, there is one other variable to consider. To present a color that looks natural a layered coloring technique is used. This is called a “base and print.” The base coat (lighter color) uniformly covers all leather surfaces. The print coat (darker color) is then erratically applied without complete coverage creating a mottled coloring affect. The technique gives the illusion of color depth, or a more natural look, resembling how a dye would render in leather.
It the case of the common question mentioned above, the tannery failed with at least two attributes: 1. Adhesion, 2. Chemical Resistance. The clear coat has eroded away and the print coat has been either worn or chemically removed (sometimes with simply water), exposing the base coat. Thus print coat failure ensues exhibiting as lighter color (the base coat) in the problem area. Often the problem is described as fading.
This is a correctable condition. It requires application of the missing print coat and then top-coating with a more durable chemistry so as to avoid the same problem from reoccurring.
As professional leather restoration and repair technicians, we see common threads of weakness in leather furniture. Typically there is a failure at some level in the basic chemical composition of the finish applied at the tannery. With an understanding of the fundamentals, we can generally develop a fix that solves the problem. However, it’s important that the “fix” itself not be problematic.
Here’s the rub. There are people representing themselves as leather repair technicians who have no clue about the fundamentals and cannot distinguish the difference between quality finishes and terrible finishes.
For example, many technicians will use colored finishes that have been engineered for vinyl or plastic. Leather is a very different material as it’s organic, not synthetic. This differential is important. Vinyl colors when applied to leather often crack and peel over time. So, it’s vital to determine if the color chemistry the technician is using is specific to leather. If the technician represents that he/she uses the same color chemistry for both vinyl and leather, then that is a prescription for failure.
To learn more about leather finishes, go to http://www.advleather.com/. Click on the leather care button. There you’ll find a description of the various types of leather and their finishes. You can also call our technical staff at 510-786-6059.
Copyright 2009 Kevin Gillan
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