Every now and then I finish a guitar and think 'that's the best looking guitar I've ever made', but the chances are 8 out of 10 people would disagree with me and choose another. This is why I love natural finishes on a guitar; because for totally illogical and purely emotional reasons, a person will always be able to choose one over another, just because that's the one they love.
You know what I think is great about the DeLorean? The stunning simplicity of keeping the bare metal look, its what makes the car truly special (along with the flux capacitor of course!). Natural finishes demand perfection because there's nowhere for mistakes to hide. It shows pride in the materials used and (when it comes to woodworking) an appreciation for the individuality of the product, because no matter what you do, you can never replicate the gain pattern and specific idiosyncrasies of a piece of wood again. Even if you're building exactly the same guitar, with the same spec, it makes each one different, each one special.
This is what I find exciting about not just guitar building but woodworking in general. I love the fact that I can't provide two people with identical products when I finish a guitar naturally. Natural finishes go from thick high gloss lacquer to rustic re-purposed wood but I've found my sweet-spot somewhere in-between and here's why.
Finishes wear and age differently, a very high gloss finish can look like the wood is encased in glass or plastic and lacks the natural feel of the wood. I'll avoid any discussion on relicing guitars here because I don't want to be greeted with burning pitchforks but a second reason is that in the hands of someone that tends to hit the body a lot when they play, a high gloss finish will look untidy very quickly. I also find that they can take away from the primary purpose of the guitar. That is to say that first and foremost its an instrument that needs to be as playable as possible and high gloss necks can start feeling sticky in certain circumstances.
Rustic finishes, for me, can also have this drawback, in that some (deliberately) rough finishes can leave enough texture that you notice it when you're playing the guitar. And secondly, rustic finishes (for the types of wood I use) don't justice to the wood itself. However I do understand how well rustic finishes lend themselves to re-purposed or reclaimed wood projects.
So what does this mean for how I finish natural guitars?
Well, firstly I'm talking about ash wood bodies, which means its an open grained wood and I also like to retain as much of the natural colour as possible, which is to say that I (generally) don't want the finish to tint the natural colour of the wood. Secondly I want the wood to be silky smooth but still feel natural to the touch. I like to see but not feel the wood grain. And third, I like a lustrous satin sheen to the wood so you can see how smooth it is, like a polished piece of furniture but not high gloss enough that finger prints and such will show on the surface, meaning it will still look as good after its seen some use. And finally it needs to be hard wearing enough that it protects the wood from wear and tear. This is my idea of a perfect finish.
So what do I use?
To get a completely smooth finish on Ash I always use grain filler. Conventional wisdom suggests that you should use an oil based filler for oil based finishes and water based filler for water based finishes however I have found over the years that (provided you leave plenty of drying time) you can apply oil based finishes over water based filler without any issues. However water based finishes over oil based fillers is not a good idea!
There are really two main types of top finishes I use, they are danish oil and hard wax oil. Both are wipe-on products and both are designed not to sit on top of the surface but to actually penetrate the surface of the wood for protection. Which one I use will largely depend on whether I want to (very) slightly darken the wood usually to compliment or match the neck colour. Secondly it will depend on the level of gloss I (or the customer) want.
Danish oil is a combination of linseed oil and varnish and is easy to make yourself (using around 1/4 to 1/3 varnish) and this tends to be the product I'll use if I need to slightly darken wood. Although you need to be careful to be sure your mixture is not going to yellow the wood, particularly for very (naturally) white woods. This is common
with oil based finishes.
Hard wax oils are a blend of oils and wax and can be bought in varying levels of gloss although even a high gloss hard wax oil will not yield the levels of gloss that a lacquer finish will give. Natural hard wax oils also tend to not tint the wood, so are perfect if you want to retain the existing colour of the of the wood. Both finishes give a very natural feel to the surface of the wood and are relatively fool proof in getting a perfect finish. They are also to much simpler than spray lacquer to get right if you don't have access to a well set up finishing/spraying area, which most self-builders don't.
That being said, any type of finish can be achieved with a little planning and effort so if you want a mirror like gloss finish that you'll have to get done in your shed, give it a go! The worst that can happen is that you'll get much better at sanding !