Colourless oil for swiss pear

[KLarsen]

Hi, 

I'm wondering what kind of oil to use for swiss pear that does not darken the wood too much. For my past model I used linseed oil which is yellowish in colour and darkens the pear considerably. This time I'd like an almost colourless finish since I like the colour of pear. 

 

Any recommendations? If this has already been discussed here I apologise, I didn't find any topic on it though. 

[Roger Pellett]

Almost 50 years ago I built an exposed frame POF model of a New. York Pilot Boat.  This was a hull model only (it was fitted with stump masts).  Materials; pear framing, keels, etc., boxwood planking, holly decking.  I had a local auto paint supply shop make up quart of matt lacquer that I sprayed with an airbrush.  The finish did not change the appearance of the wood and it has darkened noticeably with age.

 

Roger

 

 

[KLarsen]

Unfortunately I do not have an airbrush, but I suppose a spray can would work too? I'd prefer oil because it's easy to apply a very very thin layer, but I'll keep your recommendation in mind! 

[Bob Cleek]

What is it that you wish to accomplish by applying a finish to your pear wood? Preventing it's darkening will pose insurmountable challenges. Applying oil will darken most woods to one degree or another upon application, of course. (It's not a matter of applying the oil thinly with a rag. The oil soaks into the wood, rather than staying on the surface.) Regardless of what you might put on it, all wood will darken over time from the polymerization of polyphenols from lignin into tannins which are dark red or brown in color when they are highly polymerized. The specific content of the lignin in different woods affect the density, strength and color of the wood. Cherry wood, for example, may darken so quickly that care has to be taken in large jobs to keep the stock covered to prevent uneven darkening before the job is finished so the color tone will match across the entire job. Osage orange wood goes from bright yellow to dark brown. Pear also darkens noticeably. This darkening is favored in some woods which become more beautiful as they age, Honduras mahogany, cherry, and walnut, for example. Indeed, stains and dyes are used primarily to mimic the appearance of fine aged woods, which they accomplish well in the short term to the unpracticed eye, but destroy the potential of the later greater beauty of naturally aged wood pieces. Such finishes will also accentuate the figuring in some woods, of course, but that's the last thing desired in a scale model.

 

This natural darkening process is primarily a function of exposure to UV radiation and oxygen. The darkening effects of oxygen can be reduced, but not totally eliminated, by applying some sort of barrier coat fully encapsulating the wood, clear shellac being one of the most effective which is otherwise invisible when thinly applied, but the problem is that the majority of the natural darkening is the result of sunlight, rather than oxygen, so clear shellac is only of limited effectiveness. If you keep your model in a darkened environment, as seen in many museums for conservation purposes, you can slow the visible effects of the wood's aging from UV exposure. Otherwise, one would have to opt for a marine spar varnish with UV inhibiting additives, which are themselves only partially effective. However, the effectiveness of varnish with UV inhibitors increases with the thickness of the coating (eight coats being the industry standard) and, obviously, thick coats of varnish aren't what anyone would desire on a model where the thickness of the coating would destroy sharp detail. Spar varnish is also a glossy finish, so it would have to be hand-rubbed to a matte finish on a model, have a flattening agent added to it, or be top-coated with a clear matte finish. (I know of no "satin" varnish marketed which contains UV inhibitors.)

 

Bottom line, preventing the natural darkening of the pear wood in your model over time really isn't possible. If you feel it is necessary to seal the bare wood for some reason, maybe out of concern from accidental staining or to make cleaning easier (although a good case is a better investment in that respect,) a very thin coating of shellac or clear lacquer preferably sprayed on (to minimize the thickness of the coating film) is the alternative. 

 

While I realize others' mileage may vary, I would not advise the use of "rattle can" aerosol spray coatings for fine modeling work. Canned spray paint always poses the risk of a "nozzle spit" ruining the job, the plastic nozzles don't permit adjusting the shape of the spray or the amount of coating material applied, often resulting in thicker coating in corners and thinner on edges, and the color selection is limited to what's on the shelf. Canned spray paint is also extremely expensive. A good brush and properly conditioned paint applied in multiple thin coats is, in my opinion, a far better option if you don't have an airbrush. While an airbrush requires a bit of a learning curve, its use isn't daunting. I realize the expense of buying an airbrushing rig may seem beyond the budget of some, but the flexibility, results, and time savings an airbrush provides is not an unreasonable investment in one's modeling hobby and an expensive top of the line airbrush, while nice to have, isn't an essential requirement for basic modeling work. If you invest in an airbrush, I think you'll find painting a model with a "rattle can" was a lot like driving a tack with a sledge hammer. 

 

 

Edited June 14, 2023 by Bob Cleek

[KLarsen]

Thanks Bob, that's a really good explanation, I wasn't aware of the natural darkening of the wood as you describe. 

 

So is not applying any finish really a good alternative? I usually 'seal' the wood by very fine sanding and drawing a razor blade backwards over it, so it gets very smooth. But is there any greater risk of the wood warping due to temperature and humidity changes if it's unfinished versus oiled?

[Bob Cleek]

2 hours ago, KLarsen said:

So is not applying any finish really a good alternative? I usually 'seal' the wood by very fine sanding and drawing a razor blade backwards over it, so it gets very smooth. But is there any greater risk of the wood warping due to temperature and humidity changes if it's unfinished versus oiled?

As a practical matter, there isn't any greater risk of wood warping due to humidity changes if left bare rather than being coated with any sort of moisture barrier. (The expansion of wood due to temperature changes is negligible, if not purely theoretical.) Wood expands and contracts as it absorbs or expels moisture. If the wood has been properly dried and stabilized before it is worked, and the model is kept indoors where the humidity is relatively stable (i.e. not in a bathroom used for long hot steamy showers,) it should be no more prone to warping than any other piece of wood in the building. "Sealing" wood is often misunderstood. There is no practical way to completely control the movement of wood as the ambient humidity fluctuates, but if its moisture content has stabilized when worked it won't move enough to notice or to damage the structure built with it. (Grown wood off the tree needs to be air-dried for a year per inch of thickness of the lumber, or kiln-dried to reach an acceptable moisture content for the species, before being worked.) Coatings can protect against a spilled drink or a wet sponging, but there isn't any way to completely prevent moisture from "doing its thing." Humidity, like the water it is, "will always seek its lowest level." (Pascal's Principle) All that coatings can do is slow that process and perhaps reduce the extent of absorption in fluctuating humidity cycles. Actually, few coatings, even epoxies, are truly moisture-impermeable. (Surprisingly, one of the more effective moisture barriers is good old shellac, a property which causes it to be used to insulate fine wire in electrical coils even today.) You don't want to store a ship model in a wet basement anyway.

 

I don't believe there is any great advantage to putting any coating on a model built of a fine wood species that you want to present as bare wood. The natural appearance of the wood itself should be all that is required. On lesser grade wood species which will probably require staining in any event, however, a light coating of an oil, shellac, or matte coating is a good thing for appearances' sake if not overdone. It won't prevent the wood from moving with changes in humidity, though. Here again, it's a matter of taste. If you want the bare wood on your ship model to look like the real thing from a scale viewing distance, it should have a matte appearance. If you want it to look like fine hand-rubbed furniture, then, by all means, finish it like fine finished furniture. These are artistic decisions for each modeler to make as they find appropriate to each particular model.

 

One thing to remember is that in model building, as with full-size wooden boat building, wooden parts move relative to their size and the direction of that movement is primarily across the grain, not with the grain. (This property in vertical grain planking is what makes carvel planking seams swell tightly and become watertight and plain sawn planking swell against the adjacent lapping plank in lapstrake planking.) It's the soft wood between the harder "rings" that absorbs the most moisture and swells the most. Very few wood species swell much at all in length. The larger a piece of wood is, the more it will swell and shrink. Models, being made of a lot of very small pieces of wood, aren't prone to moving much at all, but improper grain orientation, particularly in large parts in the structure, can cause structural problems at times if humidity extremes are encountered. 

 

I suppose it's a matter of taste, but I favor leaving wood that I want to portray bare wood (e.g. decks) to remain bare, or at least appear so, given the frequent need for staining and weathering. At most, I give bare wood a single coat of thin white shellac for protection from staining from handling and ease of future cleaning. I suppose we have the Admiralty to thank for the fashion of bright (unpainted) wood in ship model  kit hulls these days, but, aside from displaying the intricate framing and planking of a fully-framed Navy Board style hull, I don't see a lot of point to leaving hulls bare, or even building them "plank on frame" or "plank on bulkhead at all. (It's my guess the kit manufacturers favor planking because they can pack the kit in smaller and lighter boxes that way.) A "bread and butter" hull glued up of "lifts" or even a carved solid hull, is a lot faster and easier to build than hanging plank if you're not going to show bare wood. But I suppose that's a story for another night.  

Edited June 14, 2023 by Bob Cleek

[KLarsen]

Very informative, thank you very much! 

With what you've said, I think I'll leave the wood unfinished as I really like how that looks. 

 

Again, thank you! 😀