Hightowermark:
If you want to show off the natural beauty of the wood, then you have to use a clear coat to do that, and Tung Oil or a marine varnish made from Tung Oil are probably the best choices you can make when it comes to picking a clear coat for wood outdoors.
But, the one problem that all clear coatings have is that they don't protect the wood from the UV light from the Sun very well. There are UV blockers and transparent pigments they add to clear coatings to help in this regard, but any clear coat is at an inherant disadvantage when it comes to protecting the underlying wood from UV light. Also, because UV light will penetrate deeply into a clear coat, clear coatings themselves generally deteriorate from UV light more than an opaque paint will. But, generally, the rule is that the more the clear coat stops UV light, the more it is deteriorated by it. For example, acrylic clears are so transparent to UV light that they crack and peel because the wood underneath them deteriorates, not because the UV light deteriorates the acrylic film. The UV light just passes through the acrylic film unimpeded and does no damage to it whatsoever hardly. But, that means it offers the underlying wood next to no protection against UV light.
So, take a look at the wood you're wanting to coat. If it would be a shame to cover its natural beauty with paint, then there is no choice in the matter, and you should pick a coating that will allow the wood to be seen. If, however, the objective of applying a coating to this wood is to protect it from the elements to extend it's useful life as long as possible, then you should choose an exterior emulsion paint (or maybe an exterior oil based paint). (Emulsion paints retain their elasticity much better than oil based paints, and that's important because wood outdoors will swell and shrink with changes in it's moisture content due to seasonal changes in humidity, and this one point is the principle reason why exterior emulsion paints have become the coating of choice over wood outdoors.)
But, England is in a more northern latitude, and you may not get the same intensity of sunlight (and hence UV light) and therefore deterioration of wood from UV light that you might get in more southerly latitudes, so UV protection may not be nearly as important in your case as it would be to someone living in California or Texas or Florida.
Also, should you choose to go with a paint, choose an "earth tone" color like mustard yellow, reddish brown, chocolate brown or a very dark brown color called "raw umber".
Paints get their color from solid colored particles in the paint film called "pigments". The pigments used in house paints can be devided into two broad catagories;
1. those that are made from chemicals in a lab. These will generally be easy to recognize because they will be the "colorwheel" colors, like blood red, canary yellow, navy blue, hunter green. Essentially, if you wanted to make a family of pigments from which you could produce all the colors of the rainbow, it would be best to start with the colors red, yellow and blue, and you could then mix them in different proportions to make all other colors. So, these color wheel colors are all put into one catagory and we call them the "organic pigments".
2. those that are made by pulverizing colored rocks into a fine powder. Colored rocks go by names such as "ochre", "umber", and "sienna" (which gets its name from the small Italian town where you can find rocks of a mustard yellow color. Artists like Da Vince and Michaelangelo and the great masters have been pulverizing such colored rocks to make a the pigments to mix into their paints for many millenia.
(actually, the pigments used in house paints are the synthetic equivalents of pulverized real rock, but let's just forget about that for the time being)
Rocks are very good at being opaque and even better at being old. How many things do you encounter in the routine of the day that are older than rocks? And, any kid who's ever played Hide-and-Seek knows that rocks can be useful at times because they are opaque. If you pulverize a rock to into dust, then that dust particles you make are just as old and just as opaque as the rock you pulverized.
Let's consider opacity first. Thus, if you use that pulverized rock powder as a pigment to make paint, the paint you get will hide an underlying color well the particles in it have good opacity. As a result, everything else being equal, paint colors that call mostly for these pulverized rocks (also called "inorganic" pigments) in their tint formulas will provide better hide than if that same paint was tinted with any of the organic paint pigments like blood red, canary yellow, navy blue or magenta.
Now let's consider age. It is blindingly obvious that anything that's 300 million years old HAS TO BE extremely chemically stable. If it were not, it would have decomposed by now. And that extreme chemical stability of rocks results in them both being highly "colorfast" and highly UV light resistant. (The correct word is actually "light fast" but the word "colorfast" better suggests what I want to say, which is that their color doesn't fade due to exposure to sunlight.) That is, rocks won't fade if you leave them out in the Sun.
As a result, if you use pulverized rocks to make the pigment for your paint, the paint you get will hide an underlying color better, and will fade less than if you chose a color like red, yellow or blue. Also, the pulverized rocks inside that paint are bulletproof when it comes to UV light. The UV light ray hits them, is eliminated, and the rock doesn't feel a thing.
Now, the pigments most commonly used in house paints that are made by pulverizing rocks are the "earth tones", and they are fairly easy to recognize as well. Generally, if you expect that you can find dirt somewhere in the world of that color, then it's an "earth tone" color, and that color is made by pulverizing a rock. Also, earth tones don't lend themselves to making other colors in the way that you can mix yellow and red to make orange or red and blue to make purple. Take a look at the colors in your hardware stores paint tinting machine, and you're likely to find the following:
a mustard yellow color (called yellow oxide, and is an iron oxide)
a reddish brown color (called red oxide, which is the most common form of iron oxide)
a chocolate brown color (called brown oxide which is yet another iron oxide),
a very dark brown (most often called "raw umber" which is, yep, another iron oxide)
black (which is actually soot) ((yes, really)), and
white (which is titanium dioxide).
Obviously, if someone wanted you to make an emerald green, or turquoise or pink color paint from the above assortment of "earth tones", you'd have a harder time doing it than with the organic "colorwheel" colors.
Any paint that calls primarily for these earth tone colors in it's tint formula will provide better hide, less fading due to UV light and better protection of the substrate from UV light than an equivalent paint made using organic pigments (the colorwheel colors).
Now, let's get back to that business about real and synthetic...
The pigments used to make housepaints aren't actually made by pulverizing rocks, but are the synthetic equivalent of that dust. However, because they have the same chemical composition as the real thing, their have many of the same characteristics of the real thing, and the opacity and chemical stability are two characteristics that are identical between the synthetic and real versions.
But, if I were to tell you that a reddish brown paint pigment that's the synthetic equivalent of natural iron oxide (rust) both hides better and is much more fade resistant than other synthetic pigments that are canary yellow, blood red and navy blue in color, you'd say "Really, why is that?", and I'd have to admit, I don't know.
Whereas, if I tell you that if you pulverize a reddish brown rock into a reddish brown dust and use that dust to make reddish brown paint, that paint will hide well and be very fade resistant because the dust inside it came from a rock that's quite opaque and chemically stable enough not to have changed in 300 million years, you'd say "Well, that just makes sense!" and I'd say, "Good, because that's all you really need to know to understand how the colour of the paint you choose affects the hide and fade resistance of the paint you get."
PS:
1. While the earth tone pigments are all excellent in both colorfastness and hide, thehe other thing that's worth knowing is that the organic pigments (the colorwheel colors) all vary quite a lot in both colorfastness and hide from color to color. Generally, the most commonly used red and yellow pigments in paint (Hansa or Arylide Yellow and Naptha or Toluine Red) have also been the least colorfast and poorest hiding pigments used in house paints. However, the cost of higher performance pigments (like Benzimidazilone Yellow and Quinicridone or Perylene Red) have come down considerably in the last several years, so the performance of these colors has improved substantially as more and more paint companies are using these better pigments instead.
2. If you buy your paint from a paint store, that store will have a paint tinting machine for every brand of paint it makes. So, if you buy Dulux Paint, that paint will be tinted with Dulux's colorants in a different paint tinting machine than if you'd bought a different brand of paint. However, if you buy your paint in a home center, they will use the same colorants in all their tinting machines regardless of how many different brands of paint they sell. So, if you're paying top dollar for a high quality paint, pay the few extra dollars and buy that paint from a dedicated paint store rather than a home center or hardware store. That way, the paint will be tinted with that company's own colorants, and if that company uses better pigments in their colorants than other companies do, you'll get those better pigments in your paint.
3. Be careful with white paint outdoors. The white pigment, titanium dioxide, has a catalytic effect on the process by which UV light from the Sun causes paint binders to deteriorate from exposure to UV light. As a result of this tendancy of titanium dioxide to increase deterioration by UV light, DuPont (who are the largest manufacturer of titanium dioxide pigments in North America) coat their titanium dioxide pigments with a special coating to minimize this catalytic effect. However, offshore sources of titanium dioxide who sell it for less won't have done this. This is also why many exterior paints will use zinc oxide as the white pigment instead of titanium dioxide.
4. If anyone is interested in learning more about paint pigments, or seeing some examples of organic and inorganic pigments first hand, simply drop into any place that sells artist's supplies. Any university teaching fine arts will teach their students about paint binders and pigments, and anyone working in an artist's supply store will be fully familiar with both organic and inorganic paint pigments and can show you some yellow oxide, some red oxide, some brown oxide and some raw umber so you know what these colors look like and will be able to recognize them in the paint tinting machine.
