Alternatives to the Madison Formula, 

the Original Do-It-Yourself Semitransparent Stain 

The Madison Formula 

The “Madison formula” was developed at the Forest Products Laboratory around 1950 as a simple linseedoil-based finish that could be made 

from readily available components. It

was one of the first formulations of its

type–a penetrating finish that eliminated the problems with cracking and 

peeling commonly found with the oilbased paints available at that time. 

The finish could be made with pigment to give a semitransparent stain 

or without pigment to give a water 

repellent preservative (WRP). 

Linseed-oil-based finishes that do not

include a fungicide are prone to mildew. The critical ingredient in the 

Madison formula and similar penetrating finishes manufactured during that

time was “penta” (pentachlorophenol) 

concentrate, a fungicide that was 

commonly used as a wood preservative. Penta was available from most 

hardware stores until approximately 

1985. It is no longer available, except

to registered pesticide applicators. 

Since the mid-1980s, penta has been 

used only by commercial woodpreservative treaters for treating wood 

for industrial uses, such as railroad 

ties and telephone poles. Because no 

suitable substitute for penta is available to the general public, it is no

longer possible to make the Madison 

formula. In addition, I know of no 

commercially available finishes that 

contain penta. 

It is still possible to make a water 

repellent, but the performance of 

homemade water repellents is poor 

compared with that of commercially 

available WRPs, which contain a fungicide. (See Water Repellent Preservatives.) Water repellents that do

not include a fungicide provide almost

no protection against mildew growth. 

Semitransparent Stains 

Commercial oil-based semitransparent 

stains are available in a wide range of 

formulations, all of which must comply with EPA rules that restrict the 

amount of solvents or volatile organic 

compounds (VOCs). The stains are 

formulated with or without a registered pesticide (fungicide). If the stain 

contains a fungicide, it is usually labelled as a “preservative.” Stains with 

fungicide generally have better resistance to mildew growth, though the 

fungicide is not the only component

that affects mildew resistance. 

A semitransparent stain that includes 

unmodified linseed oil is prone to

mildew, even if it contains a fungicide. Linseed oil is obtained from flax 

seed. Raw (unprocessed) linseed oil is

a mixture of several fatty acids, which 

have two interesting properties. First,

these acids are natural products and as 

such are “food” for many organisms. 

Just as mold can grow on leftover 

potato salad, mildew grows very well

on surfaces that contain linseed oil. 

Second, the chemical makeup of some

of these acids makes it possible for 

them to react with oxygen in the air to 

form a solid. For raw linseed oil, this 

reaction is extremely slow. 

When linseed oil is boiled, changes 

occur in the chemical structure of the 

fatty acids that enable them to react 

with oxygen more quickly. The term

“boiled” also includes linseed oil that 

has catalysts (also called “driers”) that 

make it react with oxygen more 

quickly. Boiled linseed oil can be

used to make finishes. However, in

most modern finishes, linseed oil is 

modified to form an “alkyd” resin, 

which makes the finish less prone to

mildew. 

Many modern commercial finishes are 

better than the Madison formula, 

particularly those that are formulated 

with modified linseed oil. The finish

should have the following attributes. 

• Be oil-based—The finish must be 

made from oil, but the oil should be 

modified to form an alkyd resin. 

• Contain about 10% to 20% alkyd 

or similar resin—If the finish contains too much alkyd, it is prone to

form a film instead of penetrating

the wood. 

• Contain an inorganic pigment—The 

more pigment in the finish, the 

longer the service life, but the less 

natural the finish. The Madison formula contained about 8% to 16% 

pigment.

	
  



	
 	
 





  	
	

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• Be solvent-based—Water-borne 

formulations do not penetrate wood 

as well as do solventborne ones. 

The use of solvents in architectural 

finishes continues to be restricted, 

and many types of oil/water emulsions are available. Because the 

chemistry of these finishes varies 

considerably, it is not possible to 

generalize about their ability to 

penetrate wood. 

• Contain a fungicide—The fungicide 

is usually listed as an “active 

ingredient” and typically has a 

concentration of 0.5%. 

• Include 1% to 2% wax or a similar 

water repellent. 

Other Stains 

In addition to semitransparent stains, 

several other finishes are marketed 

under the term “stain.” These are latex 

semitransparent, oil solid-color, and 

latex solid-color stains. Solid-color 

stains are also called heavy bodied or 

opaque stains. All of these “stains” 

form films on wood and therefore 

they are really paints, not stains. They 

do not penetrate wood well and 

should not be used in place of the 

Madison formula. 

Water Repellent 

Preservatives 

A water repellent preservative (WRP) 

is similar to a semitransparent stain, 

but generally does not include pigment. Some WRPs are tinted with a 

small amount of pigment; these WRPs 

last about twice as long as the untinted ones. 

The guidelines for choosing a WRP 

are generally the same as those for 

semitransparent stains. Avoid WRPs 

made with unmodified linseed oil. 

Solventborne formulations penetrate 

wood better than do waterborne ones. 

Some WRPs are based on mineral oil. 

Since mineral oil is not a natural 

product, it is not prone to mildew. 

These WRPs penetrate extremely well 

into wood. Because WRPs based on 

mineral oil do not cure, they can be 

applied in multiple coats and give the 

wood an “oiled” appearance. They 

usually contain a fungicide, but are 

not pigmented. 

Formulations containing a fungicide 

give much better protection to wood 

than those without one. Therefore, 

commercial finishes should be used 

rather than homemade ones. Because 

I receive many requests for a do-ityourself water repellent, instructions 

for a simple formulation are given 

here. 

Note: The following formulation 

is not as good as a commercial 

WRP and I would not use it on 

my own home or deck. 

Formulation for a Simple 

Water Repellent 

Spar or polyurethane 

 varnish* 20% 

Paraffin wax 1% to 3% 

Mineral spirits 77% to 79% 

*Spar varnish usually contains about 

50% alkyd or similar resin. If the percentage of resin in the varnish is less 

than 50%, adjust the amount to obtain 

10% alkyd in the water repellent. 

Mix the ingredients outdoors. 

Dissolve the wax in the mineral spirits, then add the appropriate amount 

of varnish. It may be necessary to 

melt the wax to get it into solution. 

Use electric heat, not an open flame. 

Pour the melted wax slowly into the 

mineral spirits with stirring. Do not 

heat the mineral spirits. 

Caution: Extreme fire danger 

R. Sam Williams 

Project Leader 

Wood Surface Chemistry 

USDA Forest Service 

Forest Product Laboratory 

For additional information, consult 

our website (www.fpl.fs.fed.us).

May 2002