If you scratch build anything with real wood, like trestles, buildings, rolling stock, bridges, and the like, and you decide to forego painting you might want to consider chemical staining.
I came across this simple process when building my first trestle which I wanted to look like the small trestles I’d seen as a youth in the Mojave Desert where a train line cut through the valley we lived in going up to the cement mines. These trestles over the dry washes were typical creosote and tar looking affairs, very dark and blotchy.
To achieve this I used a vinegar and steel wool mixture (which I call “gunk” so I don’t have to keep typing “vinegar and steel wool mixture” over and over).
The ingredients are, as you might expect, steel wool and vinegar. In this picture you can see I used white vinegar as well as apple cider vinegar, #1 steel wool (although I’ve since learned that #00 or #000 will dissolve faster) and a number of small mason jars.
I use several containers (the mason jars) when mixing up new batches as I have found that by varying the concentration (more steel wool) I get different results.
Popping some wool in a jar and filling with white or apple cider vinegar, and letting set a few days, causes the wool to dissolve.
Wanting to know more about the chemistry behind this gunk I found this posted by one of the many helpful voices on the MyLargeScale.com forum:
“The reaction between steel wool and vinegar produces iron(II) acetate and hydrogen, in the absence of oxygen.”
Now, since hydrogen is a flammable gas I always keep my mixing jars away from flames. But as was further explained on MSL:
“a pad of steel wool will produce about 1/28 of its weight in hydrogen. So 28 oz of iron will produce 1 oz of hydrogen.”
From this I gather a single steel wool pad or two won’t generate an appreciable amount of hydrogen and I have no reason to doubt the science. But better safe than sorry.
Depending on how much steel wool and how long things age the solution can get quite cloudy, which does not affect the final effect in the least. But to get a clearer solution you can always strain the liquid.
The stuff works it’s magic by reacting with the tannin in the wood and causes the wood to change colors. The more tannin in the wood the more and faster this change occurs. The principle advantage that this process has over others is that, unlike paint for example, it won’t flak, peel, or otherwise come off the wood. It will age along with the wood and the results I find to be very good.
For my trestle building I use the cheapest redwood fence boards I can find at the big box stores and I stain the wood after assembly with gunk. This pictures shows a piece of trackwork from a curve I was building with the right hand side stained and the left “natural”.
The wood is bit shiny in this shot since after the chemical staining I dipped everything in motor oil since this was going outside.
Again, the amount of tannin in the wood produces the effect. So cutting stock from several different boards and mixing up the pieces will give you a more varied look.
I’ve also used this technique on craft/popsicle sticks. They tend to stain more gray than black and by changing the concentration of the solution when applying to various pieces (I “paint” it on using old and discard-able paint brushes) I can get some nice variations in appearance.
The stick at the top is a redwood tie (1/2 x 1/2 x 6 inches) you can also see test dippings using craft sticks (the tongue depressor size) as well as two small pieces cut from your typical coffee stir sticks.
Here you can see the side of a covered bridge I build and how the craft stick siding looked after weathering using gunk.
If you have any favored weathering techniques for wood let me know. –TJ
(Originally posted 6/10/2011, revised 3/15/2013)