I put a cheap plank of almost white new pine in the garden a couple of months ago - the grain is now far more visible (while not being raised) and the base colour has darkened. I would like to replicate this effect with boring-looking pieces of pine flooring so that newer boards closer match those laid over 100 years ago, but in a much shorter period of time. Thanks in advance for your insight.
...the grain is now far more visible (while not being raised) and the base colour has darkened. I would like to replicate this effect...
There are many tricks and techniques for creating an aged look, from chemical stains to ammonia fuming to UV tanning beds. The trick is to find one that produces the look you want on the wood you've got.
A lot of the techniques you'll find for darkening wood rely on chemical reactions that involve tannins. I'm sure you've heard of tannins -- they're the chemical compounds that give barrel-aged whiskey it's color it's color, that make red wine astringent, and that turn animal skins into leather. They're also the reason that some woods get black stains when iron pipe clamps meet glue squeeze-out. Wood species vary in their tannin levels, with oak and walnut containing lots of tannin and pine having less.
If you want to darken your pine flooring, the pickling process that involves combining tannins and iron might be a good bet. Because pine has relatively low tannin levels, people generally add tannin to the wood by first brushing on some strong tea, which is high in tannins. After that, a solution containing iron (made by soaking steel wool in vinegar) is brushed on. Lee Valley has a helpful article about pickling wood this way, and this blog article has a specific recipe and a photo showing results. The reason I suggest this method is that you can easily adjust it to get the results you want. You can change the amount of tannin that you add to the wood by using stronger tea or applying the tea more than once, or you can replace the tea with a solution of straight tannic acid (which might give more repeatable results). Likewise, you can change the concentration of iron in the vinegar solution.
There are really two parts to aging wood: coloring and physical mark-up.
To age brand new pine wood (2X4's in my case), I started with a flat head screw driver. Marked up the pine by hitting it at different angles of the head. Also, did a few deep scratches up and down, a few inches. Next, took an adjustable wrench with the adjustable part sticking out, beat the wood with it. Took a random strangely shaped piece of metal I found laying around and also made marks with it. Then took the side of the screw driver and hit the edges to get them "down", at least in some places.
Next, took a back of a hammer and actually cracked parts of the wood & dug holes in it. The digging looks very close to the natural "missing pieces of wood" (forget what that is called, knots?), but that may be too much for your garden, not sure what you are trying to match looks like.
All these methods were sprinkled on, as it all adds up fast, less can be more.
Color; First tried the vinegar with steel wool thing. While it looked okay...I decided to go with a stain. After the stain dried, I used liming wax. This worked really well, as the liming wax hits the cracks and wholes. Not sure if the wax will stay out doors so you could use a vintage white paint also.
When done, it looked very close to what I was aiming for.