Stain Chemistry, Solvent Content, Drying Time, and Adhesion

Here's a highly informative, in-depth look at oil-based stain chemistry, along with some de-bunking of the conventional wisdom concerning application windows. May 18, 2010

This seems to be something that comes up all too often on the forum. I have read people saying it's "full of oils" that they add "japan driers" to make it dry faster, and etc. If you look at the MSDS for min-wax stains you'll see it's no more than oil soluble dyes and micro pigments in an aliphatic and aromatic solvent blend.

Petroleum distillate - 0-3%
solvent naphtha - 87%
Stoddard solvent - 0-12%

Although in the industry aliphatic's are considered oily feeling and are made by fractional distillation of petroleum, they are not oily in the sense that cooking oils or even car oils are. It just means they distilled from oil (not fats). Aromatics on the other hand are distilled from coal/coal tar by destructive distillation. They have no oily presence in them when rubbed between your fingers, nor do they leave any oily presence on that which they are applied to. Aliphatic can be totally dried out with the aid of heat leaving only trace oily characteristics if their particular boiling point profile is such to allow this. None of the distillates in min-wax are such that would cause this. Two are in the category of mineral spirits (as to boiling points) more or less and the main solvent is an aromatic.
This is necessary because the oil dye which really is not an oil soluble dye, dissolves much better/completely in coal tar derivatives (lacquer solvents) for example. For example: if you took dry oil soluble powders and put a tiny amount in MS or Naphtha (VMP), the color would be very slight and undisolved residual would sink to the bottom, only a small percentage dissolves. But in butyl acetate/acetone/methanol/toluene/mek/etc, it would be very bright and totally dissolved so the name oil soluable is really a misnomer.

Minwax uses these dyes from diff mfg.'s to do just that - give a reasonable dye color of mid saturation point and mixes them with micro pigments for enhancing the grain. This is normally called popping the pores by making them dark and also adding some color to the wood surface that the dye is not capable of doing since it will not hold on to the hard lighting structure of the exposed sides of the pores/cells in open grain woods such as oak/mahog./ash/etc. Though it's better at this than water dyes that do not stick to lignin walls at all, therefore leaving dark colored wood with natural looking or bare color pores. Cold weather will affect all stains made up of aliphatic and aromatic solvents, but more so the aliphatic. These can be force dried like in the factories or in a pinch dried carefully with a heat gun hair drier if need be to bone dryness in minutes.

Adding Japan drier to a drying or semi-drying oil affect's the oil in this way - the drier is mainly cobalt which has an affinity for oxygen and brings oxygen to the oil to hasten it's drying, it is usually a surface dry it gives and not a through dry, for that you need an intermediate dryer like aluminum or a combination of both. Since there is no drying oil that dries by oxidative methods in the minwax stain the addition of it or use of it is an absolute waste. Oil dyes are available in two main types - dry powder which you dissolve yourself or in liquid form such as keystones. In either case, there are no drying or semi-drying oils present unless you have yourself added them, if not then no oxidative reaction will take place nor quickening of the drying procedure. Looking at the evaporation rates of the three solvents in minwax stain I see nothing denoting excessively slow (take's days or weeks to dry) culprits, if there is a culprit for slow drying it definitely is the cold temps and low or no hot air airflow!

In Florida I often sprayed over minwax when the customer insisted on that product within minutes after applying when temps were in the 80-90's without ever experiencing faulty adhesion. If it then can be sprayed over minutes after application in those circumstances without decreased adhesion then it's not a matter of absolute "bone dryness" being needed but high temps and good air flow to achieve what’s desired. You are more than welcome to try this come summer on a nice hot day of 80 or more then test for adhesion the next day or so.

Using shellac over minwax has also never been a problem for me though rarely done for there is little need for it unless I know there to be contamination of some type like fisheyes etc. For a clear pine, this is not necessary nor for other woods like maple/birch/mahogany/walnut/oak/ask/etc. Therefore if you plan on using water-base over such there really is no need for it being your first coat unless you know that your product will behave strangely if you don't barrier coat it with shellac. If that is so, I would rather you look for a new product that does not do so and save the time and expense, but that's up to you.

Forum Responses
(Finishing Forum)

From contributor G:
Thanks for all that information - very informative. As an aside, during the summer two years ago I had floor guys redo my oak flooring. They applied minwax stain, then within an hour went over it with sealcoat. When it dried they put on the finish. I was aghast, figuring the minwax needed to dry thoroughly. Not a problem it seems.

From contributor Y:
I can't wait to hear more on this one. The initial explanation goes completely against what I've ever been told regarding Minwax. I use Minwax often, with shellac after 24 hours, then WB varnish 24 hours after that. So according to the initial post I can seal with shellac a few hours after staining providing there is good heat and airflow?

From the original questioner:
All of my points being made are with the use on my part of evaporative finishes mainly shellac/nitro/and mostly acrylic, which is a big player (or was) in the south Florida region for a long time and when I left in 07.

Any water-base should be sampled first under what I have said to know for sure that there will be no problems. To many different additives to know for sure to make a blank statement here. The ones I used acted as I have stated. I don't recommend you blindly try this on a project - run samples first as always with your products. I'm also not recommending you put water base over a freshly stained surface, that will require a complete dry if you’re not using shellac barrier. Any first coat of WB should be put on thinned out for best adhesion. As I have found out, this allows for some penetration of the resin into the wood surface much more than an un-thinned coat.

From contributor M:
Why not just use the MLC stains? They are available in Minwax colors.

From the original questioner:
I don't use either - I make my own and can manipulate as I deem necessary. I brought this up mainly because of many posts I read or have seen on this product that evidently is either more widely used than I thought - maybe because of easy access to it - more so than because of its wonderful properties. At most it is a passable dye/stain and at least a very costly product that can easily be made by anyone with a little R&D.

Drawbacks - has medium fade resistance in between alcohol and water dye/stains. Limited color choices, and leads to dependence on its availability for continued use by those looking for easy color matching venues. That's why we’re running out of problem solvers in the industry outside of the chemist themselves. We are depending on premade prepackaged finish items to do away with having to learn color matching/coatings/chemistry and all else.

From contributor O:
I don't know about the theory, but I do know that Minwax stains generally take too long to dry, with the work taking up too much precious space in a small pro shop environment. They will bleed out of open pored wood for days, despite frequent wiping and forced air drying. I also remember that I had blushing and adhesion problems under waterbased finishes.

My conclusion was, I don't need this hassle, and with MLC offering the Minwax colors in a fast drying stain, I don't have to put up with it. If I need a true oil based stain to pop grain etc, there is a local manufacturer in Toronto that produces a very high quality product.

From the original questioner:
I'm not hyping up the use of min wax. I have only used it when it was either the only thing in a shop or specified directly by the client. Things your bringing up are very true as to bleeding and seeping. It's also true of other oil soluble dye/stains. Like I said they are only adequate at best for shop use. If I needed them for something I would make up my own rather than use the off the shelf products. Here again my use was always as I stated in very hot south Florida weather with good airflow in the open door shop(s). I would, like you, rather see everyone use better stains/dyes than minwax. This post was only to inform for better use and understanding for those who are using it.

From contributor F:
I find this post very informative. I don't use Minwax as I find them to be more hassle than they're worth and they don't really give you deep colors. I've been using mostly Mohawk and ML Campbell's stains and I'm getting to the point where I'm not that fond of them either.

Therein lies the problem, you can get to a point where you realize something off-the-shelf isn't going to give you the results you want, but how do you get them? I'm in that stage where I'd like to know a lot more about finishing so I can be more flexible. I have Flexners' book but I find it's geared more towards hobbyists than anything else. I also spent a day at one of ML's finishing (glazing) classes and though I didn't expect to come out with perfect results, I found the end product pretty poor. Worse I didn't really get the information I wanted to help improve the results.

On a recent project I spent two days working at getting the color I wanted. In the end I got it, but it was a seven step process of sealers, dyes, and an off-the-shelf stain to get there. Certainly not anything you could get with Minwax, and it shows. But I'm thinking if I was a little more knowledgeable I could have probably cut the number of steps down a bit.

From the original questioner:
I understand your frustration. In Florida in the 90's I had a company whose finisher had created a whole line of finishes that revolved around one Mfg.'s glazes and stains and dyes, etc. This is not unusual but the problem is that company was bought out by a larger company and the products became unavailable.

The finisher tried many other products to come up with the same look and usable techniques he developed to apply them. It never really worked out and new samples/catalogs/and finish options all had to be worked out all over again. Now this is not unusual at all it happens quite frequently, (the discontinuance of products). This is why I write to get people to learn how to make their own glazes/stains/dyes/fillers/etc. If you’re in control of the colorants and vehicles necessary to produce these, then you have a great advantage over those who do not. By this I mean no one can hold you captive to their material offerings. You control how they work and are applied and dried and used overall - not some chemist or tech. You also don't have to be subject to attending seminars or schools that mainly teach you how to use their products which locks you in to continued purchases from them.

What use to be the normal was a internship/apprenticeship for people interested in this trade (and others) to learn from a master finisher (one with decades of experience) on how to mix colors/color theory as applies to decorative and protective coatings, the makeup of and formulating, and application of all the products found in the shops at that time as well as the repair and care of such. Also you would be taught at least basic chemistry of what strippers or coatings were and their use and myriads of other side info with hands on teaching and overseeing of your trials as you started to do these things yourself.

The people I loved training more than all others were those who really were just normal people with a fascination with the art and were eager to learn and had just good common sense and teach-ability. In fact the less you know when you first become interested in this art the better off you are if you can find someone to train you. There are no bad habits to break, no ego's to contend with - just those with a deep desire to learn all they can.

So past min-wax, or others color offerings, I urge you to study color theory as applies to our industry, the components that make up glazes/stains/dyes/coatings/and all else that pertains to this artful craft. May your success be a happy endeavor and lifelong satisfaction of creating beautiful wood finishes.

From contributor U:
It's always been my understanding that stain includes a binder but there was no mention of one in your post. I looked at an old can of Minwax stain and didn't show anything except the typical 'Rags may..." which often indicates linseed oil. So I looked up the MSDS and found: Product type: Alkyd Stain. Mystery solved.

However, as I was glancing down the list of ingredients I noticed the Aliphatics, didn't see any Aromatics and then something which I do not understand:
Heavy Naphthenic Petroleum Oil 6 - 9%
Highly Refined Naphthenic Oil 6 - 9%

Never heard of it and couldn't find out much about it except that it is apparently used to cool tranformers and fill shock absorbers?

I also noticed that they list: Cobalt 0 - 0.2%

So my questions are: what can you tell us about Naphthenic oil? Is it a drying oil? If Minwax adds cobalt to their stain why would it not be ok to goose it a bit a with Japan Dryer?

From the original questioner:
Unfortunately the MSDS does not put the binders on it because they are not usually volatiles. But you’re right - it is an alkyd binder. If it already contains cobalt it would be at an amount that was already determined to be the best amount for the formulation, adding more is not going to do any or much good and just increases the amount of non necessary toxins in the coating. Seeing that it is there means that it's a semi drying oil or drying oil needing an added metal to dry at a usable speed for use. There are no aromatics in the stain, this is because they are using a liquid dye supplied to them not a dry powder. The liquid dye is already solved in aromatic solvent, usually but not always toluol. Others are used depending on the nature of end product required by the buyer, for instance candle makers might use an aromatic naphtha for incorporation in the wax, etc.

If they list the CAS#'s I can look up the oils you refer to for better in site, off the top of my head N oils can be both drying and non drying this will depend on where the fractionation points are in the distillation and what the intended use may be for the product.

Contrary to popular belief a binder is not necessary for making a pigmented stain that is going to be wiped or sprayed on and then all the excess wiped off, it just makes it easier for use. Buy some pigment form the art store and mull it with mineral spirits and rewet as necessary. Apply to the wood let the MS evaporate and you will see that it looks just like one with a binder. You can also spray over it quicker than if you had a slower drying binder in it. On large jobs there’s lots of surface to cover. The alkyd/Blo/acrylic or other will act as the binder, and keep the otherwise dry colorant/solvent that might wipe off in place, but it's not necessary, just easier.

From contributor U:
It's not nonsense to add a little drier to the stain to help it dry faster. Japan Drier works well; that's why they sell it at the home centers and paint stores (though it's most often used for oil-base paints but the chemistry is equivalent for oil-base stain) and why I recommended it. Oil-base driers don't contain lead anymore, so toxicity is far less of an issue than it used o be.

I thought it was very odd that the MSDS stated the stain contains non-drying, petroleum distillate oils. It really doesn't make sense to me and I don't believe it's correct. If it was, that would mean the surface would remain oily no matter how long it dried even if you added Japan Drier. I contacted Minwax and asked for the MSDS and they told me I could get it from The MSDS at paintdocs only lists mineral spirits (53%), odorless mineral spirits (5%), and titanium dioxide (TiO2). TiO2 isn't listed in all the MSDS they have for oil-base stains because some of the Minwax stains are colored with drying oil like linseed oil, or a combination of both. But the MSDS contains this warning in Section 7 - "To minimize the possibility of spontaneous combustion: control the accumulation of overspray; soak wiping rags and waste immediately after use in a water-filled, closed metal container; air dry filters outside, far from any combustible material and separated by bricks or other non-combustible spacers; dispose of all contaminated materials and waste properly." From this statement we can determine the stain must contain an oil-base binder because spontaneous combustion occurs when heat is generated during the autoxidation process. Minwax does contain an oil-base ingredient that dries through -linking-film-formation oxidation. I'm not sure if it's an oil-base alkyd, a drying oil like linseed oil, or a combination of both. But the MSDS contains this warning in Section 7 - "To minimize the possibility of spontaneous combustion: control the accumulation of overspray; soak wiping rags and waste immediately after use in a water-filled, closed metal container; air dry filters outside, far from any combustible material and separated by bricks or other non-combustible spacers; dispose of all contaminated materials and waste properly." From this statement we can determine the stain must contain an oil-base binder because spontaneous combustion occurs when heat is generated during the autoxidation process.

All pigmented stains do need a binder to attach the pigments to the wood. The binder in consumer friendly stains like Minwax has to be pretty strong because they are often topcoated with wiping or brushed varnishes (hand applied finishes). As the binder in the stain cross-links, it becomes durable enough to withstand the solvents in the finish that's applied over it. That's why the stain dries slowly and even more so when the temperature is cool and the humidity is high. The productions stains professional finishers often use (e.g., WoodSong II) don't have such a strong binder and can dry much faster since they don't need time to crosslink. But you can't apply a hand applied finish over them because they will dissolve and smear; you have to use a spray applied finish over them.

Dyes are the most lightfast (resistant to fading), but that information is out of date. Today there are metallized acid and solvent dyes that are more lightfast. When you buy water-reducible dyes you may not know if you're getting basic dyes that fade fast or plain acid dyes that are better but still not as good as the metalized dyes. A number of other topics have been introduced in this thread as well and I think it's always a good idea to research the information you find to verify the accuracy and learn more if you're interested. I'm not singling out any individual with this remark. I'd encourage folks to look up the information I post along with any other. There are lots of myths in wood finishing, outdated information, and other assorted mis-information to be found. For a solid background in the basics, I'd recommend Bob Flexner's book "Understanding Wood Finishes" and Jeff Jewitt's book "Complete Illustrated Guide to Finishing." You can find some good information is some of the older books. For example Sam Allen's "The Wood Finisher's Handbook" has some recipes for making your own stains and his book "Classic Finishing Techniques" has lots of info on natural and chemical stains. But these older books, and even some that aren't so old, have incorrect information in them. As an example, a lot of the finishing books say that water-reducible dyes are the most lightfast (resistant to fading), but that information is out of date. Today, there are metalized acid and solvent dyes that are more lightfast. And when you buy water-reducible dyes you may not know if you're getting basic dyes that fade fast or plain acid dyes that are better but still not as good as the metalized dyes.