No-blotch dying

Methods to achieve uniform finishes. March 5, 2003

Question
I am trying to deal with softwoods and woods that tend to blotch when stained.

So far, my best method is to dye the wood before a wash coat. What type of base should I use with the dye - water or oil? I am guessing that when using a water based dye, it would be best to pre-wet and sand the wood before dying. Next, the wash coat (I'm assuming sanding sealer here) - there are lacquer sanding sealers and varnish sanding sealers. Does it matter which one I use with an oil based stain (after the wash coat) and then the final finish?

I'm in the middle of a cabinet using p. mahogany (by mistake), and would like to use it up before never touching the stuff again.

Forum Responses
(Finishing Forum)
From contributor B:
Water soluble dye is the most colorfast. And yes, you should do a grain raising procedure prior to application. If you use water soluble dye you can go right with oil base finishes without a sealer. A sealer is necessary when using a waterborne finish with a water soluble dye; it activates the dye.

From the original questioner:
What about blotching? Does the water base with the dye somehow lessen the possibility of blotching (perhaps closing the pores up more or something)?

Water-soluble dyes are not exclusively the most lightfast dyes - this is an old, old piece of info that keeps circulating like an urban legend. It is in fact rare to find dyestuffs from the key players in the game today that do not have a good to excellent rating when it comes to lightfastness. Also, individual chemicals (mordents) are used to set or activate dyes, not finishing products.

You will notice that many companies offer dyes that make about a quart of stain per dry ounce of dye, but this typically indicates that the dyestuff has been cut or is of a lower quality. Aim for products that indicate that 1 oz = 1 gallon of stain.

Russ Ramirez, forum technical advisor

Blotching with water base aniline dye occurs more when you wipe on and wipe off the stain. This pushes more dye into the softer wood. On blotch-prone woods whenever possible, I spray on the stain as evenly as possible (like shading) until the surface is wet evenly but not puddled, and then just let it dry. Sometimes, like inside cabinets, this is impossible unless you stain and seal the pieces before assembly.

From contributor B:
Stain causes most blotching, not the finish. The reason is that stain particles are larger and are absorbed differently in soft or hard portions of the grain. Dyes are microscopic and are absorbed evenly in hard and soft portions of the grain and don't result in blotching. Also, I believe a certain finishing expert (Mr. A) when he says water soluble dyes are the most colorfast. And I also buy his dyes.

From contributor M:
It's the woods that cause the blotching - the dyes and pigmented stains only bring it out. If you only clear coated the woods, you would never see blotching. The problem with blotching is you don't see it until after you stain the woods.

Pre-conditioners, sealer coats and glue sizing may all work when applied properly, but not too many shops want to use these mediums on every piece they finish, and as I said, you can only see the blotching after it's stained. So it becomes "should I or shouldn't I?".
This is one of the biggest reasons for doing factory finishes using toners - you never have to worry about blotching. To get true transparent finishes, a little blotching isn't that bad after all. It's natural - it's in the wood!

From the original questioner:
So, if wiping a dye also has the tendency to cause blotching (right, but not as much as pigment?), then I should spray the dye onto the work and not wipe off. If this is the case, would it then be better to use an alcohol base dye or just stay with water?

I never favored the idea of toners or shading due to the scratch and nick repair complication. I also favor the idea of transparent finishes.

From contributor M:
Yes, let the stain dry itself.

The big difference in spraying the water and alcohol stains is that the alcohol stains dry much faster and do not raise the wood grains.

You're not the only one who doesn't like toners - they are not for everyone. They certainly have their place in finishing, just like the pigmented stains. It depends on the type of finishing you're doing.

From contributor E:
Contributor B, I have to take exception to what you have written, particularly this quote:

"Dyes are microscopic and are absorbed evenly in hard and soft portions of the grain and don't result in blotching."

That just is not the case. Dyes are microscopic but they do not absorb evenly into hard and soft woods. Neither do they eliminate blotching. In fact, they can intensify blotching! The wood itself (and wood species to some degree) is the culprit and will determine to what degree blotching is a problem. Along the face of the board, how the fiber orientation presents itself at the surface of the board (where the stain is applied) is *the* determining factor of whether or not the surface will display severe, minor, or no splotching at all. Different wood species are known to be more or less problematic as far as this is concerned. For that matter, it is not so important whether the stain is a dye or pigment, or a combination of the two - as most ready made (hardware store type) stains happen to be.

I don't know what Mr. A had to say exactly, but could it be that you have misinterpreted him? I expect that he is well qualified (better than I) to know that what you have written is not completely accurate.

To illustrate my point, take any light colored, hard or soft wood, sand it thoroughly, and apply whatever (preferably dark) stain that you desire, saturating all surfaces of the wood completely with the stain. Look at the end grain on that board and you will see a drastic difference between the color intensity between it and the face of the same board. Why is this?

It would be nice if all trees started out on flat and level ground and grew perfectly straight to the heavens, with no branches reaching out away from their trunks. Nice too if the sawyers in the mills could follow precisely along the length of the wood fibers, severing through none, as they produced one perfect and consistently surfaced textured board after another. But this is obviously not possible and I think not even desirable, because there are not many objects in this world that are more beautiful than a well figured, beautifully finished natural wood product.

From contributor M:
Let us not forget the end grains which are notorious for blotching, and we can include the routings as another blotching factor.

What Mr. A may have said or wrote was that his new dyes are more colorfast in comparison to the older aniline dyes.

From contributor E:
I wasn�t very clear about what I intended to write. By using the end grain as an example, I intended to illustrate that the end grain (and routed edge for that matter) is an easy to see and understand example of what the primary cause of blotching or �splotching� is, by my understanding. A very similar effect occurs when the log is cut at the mill and the wood fibers (in certain areas of the board) are sawn through, either on a bias or perpendicular to their length. When the cut travels through an area along the length of the log where a branch once grew, or where a burl was contained, or some other such natural characteristic (or defect) in the log, we often celebrate these features and describe the board as �figured�.

If the dye stain is shot from a spray gun (as I prefer to do) then it is much easier to control and minimize splotching by making very light passes, directing more or less stain over certain areas of the surface to help even out the color contrast across the entire surface being stained. This is less easy to do by hand application with dye stain alone, as a full saturating coat is most often required in order not to leave �dry� spots, or areas across the surface.

Blotching is caused by uneven density in the wood. It is not caused by a particular stain or dye. Softwoods are more prone to this, but some hardwoods such as cherry and maple will also develop these areas of seemingly random density. No matter what coloring medium you use, pigment stain, dye or a combination of the two, the wood will blotch because the more porous areas will soak up more color. Even with dye's microscopic particle size, more color will be soaked into the areas of softer density. The reason dyes have a reputation of not blotching is if they are *sprayed lightly*, and built up in numerous coats, they will dry on the surface of the wood and not be soaked into these soft areas. (This is the same reason that gel stains don't blotch as much - they don't penetrate the surface of the wood much, so they blotch less.) If you spray a dye too wet on a blotch-prone wood, it will blotch. Lightly sprayed dyes rarely look good by themselves, though. This is the reason for washcoating and using a wiping stain and/or toners after spraying the dye. This evens out the foggy look that lightly sprayed dyes can get. Now, some dyes may look better than others when sprayed on and some wiping stains will blotch less than others. I've had fine results with Behlen Solor Lux dyes, as well as MLC's Mircroton dyes and Sherwin Willams' Sherwood wiping stain concentrates. The concentrate can be mixed as thick as you like with the clear stain and is less prone to blotching when mixed at a thick ratio.

I did a test on some African mahogany I just planed. It was bought off the same pile but when planed, some of it was lighter in colour and weight. The lighter material in the test went blotchy while the darker, heavier material did not. I have a choice - spend a wack more on material till I get enough of the darker material or play with the stuff to eliminate blotch! I hate playing with toners! It's one of the reasons I won't stain maple.

From contributor D:
How many times do I have to tell you fellas? Glue size.

From contributor E:
One of these days I'm going to have to order me some of that "glue size" stuff. If for no other reason than to complain about it to you :-)

I have a simple, highly consistent solution for splotch prone woods that I use, and it is reasonably priced and available nationwide - but I ain't gonna tell you what it is 'cause you'll just make fun of me... Hint: I believe you once gave me the formula to make the concoction myself.

Contributor D is right-on and since some degree of sanding has to be done anyway, there's not much of an excuse for not sizing the wood before coloring it.

As a personal preference, I believe that light-colored dewaxed shellac like the Zinsser SealCoat product or a wash coat of lacquer is the way to go in terms of its value added to the appearance of the work.

Russ Ramirez, forum technical advisor

From contributor M:
Russ, second opinion. Depending on what stain and the type of coating being used, in some cases the glue size is a better choice. Once the glue sizing has completely dried, it is also a terrific barrier coat for any type of stain or coating.

From the original questioner:
I'm now hearing a lot about glue sizing and washcoating. Would it be better to lightly washcoat before the dye (since dye will also blotch if not careful) or after, in case I want to add some pigment for the grain (and just be real careful when spraying the dye)?

Also, what does everyone recommend - water based dye or alcohol based bye?

My plan so far is to spray dye, washcoat, and if I can't get the grain I want, washcoat, then wipe on some pigment stain. Then cover the whole thing with poly. Can anyone better this plan? Again, I'm using p. mahogany and am trying to doctor it up to make it look as close to the real stuff as possible (before I never touch the stuff again).

Washcoat, sand, spray the dye, seal, stain, sealer and topcoats.

Russ Ramirez, forum technical advisor

From contributor D:
Why glue-size is good is the same reason shellac is such a killer sealer and that is because it uses a different solvent system. Glue-size is water based, which is why you need to use alcohol dyes with it. Water dyes would dissolve it, defeating the purpose of using it as a barrier coat.

Let's go with first principals. The idea is to harden the soft parts of the wood, which are those that will splotch. Glue-size being waterborne deeply penetrates this softwood and reduces its absorption of stain. Since the stain is not able to resolvate the glue-size (solvents will not dissolve it, only water does), blotching is thereby prevented. This mixing of solvent systems is a key to effective barrier coats, which is what you're really trying to accomplish here. Shellac is the all-time best example of this concept when used as a sealer. Nothing attacks it except alcohol, so waterborne and solvent borne go on top of it without dissolving it. Chemistry is a thing of beauty.

And yes, contributor D, I do remember providing you with Chris Minick's pre-stain conditioner formula. In that case the key is saturation, which is why you need to come back with the stain before the pre-conditioner dries. You use his conditioner to load up the pores of the wood so that the stain can't be overly absorbed. Different idea that also works.

There are a number of other resins that will do the trick as well, but some that may be already on the shelf for some folks are the waterborne acrylics on the market that don't raise the grain of the wood. This way you get the benefits of an NGR material and the solvent resistance. Examples would be the Fuhr 355 or the VanAqua 280 products (there are a number of others).

Russ Ramirez, forum technical advisor

From Mr. A:
If I said that water-soluble dyes are the most colorfast of all the dye types, it may have been a long time ago. The old classifications of water, alcohol, oil to categorize the performance of any specific dye should be thrown out the window, as Russ points out.

Lightfastness is determined by the chemistry of the dye, not what it dissolves in, and there are plenty of water soluble dyes that have no lightfastness whatever.

As for using water dyes to control splotching, it's just one of the many methods you can use, but you can get splotching with water dyes, as with any colorant. In a general sense, water dyes tend to de-emphasize grain. In a commercial, production setting, washcoating is certainly about the most foolproof.

I think in many ways a balance needs to be struck between eliminating color variance and good finishes that reflect depth and interest. You can get to a point in eliminating splotching where the wood looks like Formica.

From contributor D:
That's a good point. When I started finishing I considered splotching the figure of the wood. Go figure. I remember proudly showing my friends the beautiful variations in the dresser that I had made and then realized it was splotched (oh the horror!).

The problem is that Ethan Allen and everybody else that makes production furniture has used multi-step finishes to reduce wood to a uniform commodity like laminate.

Speaking of laminate, I just finished a modern table for a co-worker that required that I buy some black wood grain laminate from Wilsonart that has a perfect oak wood grain texture to it. They call this finish cathedral and it was perfect in every way. It was also plastic and not wood, so we need to ask "Where do we stop?"

The comments below were added after this Forum discussion was archived as a Knowledge Base article (add your comment).

Comment from contributor M:
I often use a light spit coat of clear or amber shellac - mix one part shellac to about four parts denatured alcohol. Put this on the piece, let dry and then stain over. The open or more porous grain will take the shellac and the stain will go on evenly. Also use this method to treat end grain - but you might have to do it twice (on the end grain only). If the wood has an open texture (porous) then you will still need to fill the grain with paste filler or whatever you prefer as the shellac won't be enough of a base when applied this thinly.