Care to weigh in on finishing with mineral oil + a hardening finish?

[George Overpeck]

Hey all - I'm looking for thoughts on a finishing program I have in mind.

I've been doing some mid-thin work that looks fairly nice with a deep penetrating finish, there are some translucent areas of heavy spalting and the whole piece can look generally great because of the ability to see into the wood. I've been using my own variation on the hawaian style of immersing the piece multiple times in the finish- I'm using lacquer while they are using poly or danish oil mixes.

When I do this dipping finish the work comes out of the bath saturated (and pretty!), then it cures and becomes less pretty, goes back in and comes out pretty, and dries slightly better with each dip. My idea of what is happening is that the lacquer deep in the wood is becoming thicker with each cure cycle until I have a very high penetration of dried laquer, it gets a surface finish and it's good. The attached photo is an example of this coming out well in terms of translucence, depth and clarity.

set .jpg

Attachment 278613
So, looks great but time intensive and more relevant, it's tough to do at this time of year in Alaska because it's off-gassing too much to cure inside and too cold to cure outside. Even if I put pieces in the greenhouse I've only got a few hours curing time on a sunny day. They take a long time to cure because you are migrating the solvents out of a lot of lacquer.

I was thinking of oil combinations as an alternative - mineral oil + a polymerizing oil as a topcoat, or mineral oil + lacquer, shellac etc. I thought I'd check in with the SMC community before I started throwing money around.

Here are a few things I suspect about mineral oil that I might be wrong about, feel free to correct me if so-

- I've read that it has virtually no evaporation at room temperature. So, maybe the need to refresh a mineral oil finish in treenware comes mostly from the oil's continuing migration into and distribution in the wood + handling rather than "drying".

- wood can absorb a lot more oil than "once a day for a week, once a month for a year" can put in it.

- the "muddying" aspect sometimes associated with mineral oil come more from the wax which is usually used with it which collects any particulate matter it contacts.

I guess my questions are these - how do you think appearance would hold up 5 years down the road in a piece which was saturated with MO, then given a surface coat to seal it in? If you think the oil would break down or evaporate, could it be mixed with the next less volatile product up the chain, paraffin?

Do you think that MO would give the same amount of translucence as a hardening finish? I've been wondering if the immersion technique is so attractive because the hardened finish is somehow propping open the fibers to let light pass through.

Also, I'm not stuck on MO. I'm just looking to minimize fumes while getting maximum penetration into the wood.

Thanks for reading so much, looking forward to hearing your thoughts!

[Jon Nuckles]

Cannot address most of your questions, but my experience with mineral oil by itself is that the piece looks nice and has some depth and translucence but dulls over time even if it not washed or handled. Fwiw, the piece was cedar. Good luck with your experiments and report back.

[Richard Coers]

First thought, you will have to let mineral oil dry for a long time before surface coating, lacquer? I think a lot of these guys use a penetrating oil finish because it is more tolerant to moisture in the freshly turned wood. Lacquer and damp wood isn't going to work well.

[John Keeton]

Since mineral oil is typically used as a "release agent" in many applications - preventing adhesion of various substances, applying a film finish over it would just seem problematic IMO. From my understanding, it never polymerizes (cures) and remains in a liquid state.

Why not try another oil that "cures" - tung oil, or BLO, both of which polymerize though at different rates?

[Thom Sturgill]

One of our club members makes beautiful translucent NIP pieces. Repeated soaks in BLO, cure for a month, and lacquer over that. He does not have a tank so he pours it inside and sloshes it around pours that out and brushes oil on the outside until it will not adsorb more, let that soak in and cure and do it again about 5 times.

[Reed Gray]

Well, the mineral oil never dries or cures, so it offers little protection. Walnut oils will cure, like Tung and Linseed, but it takes a while. They penetrate, then cure and harden. This type of oil (Mahoney's or The Doctor's Woodshop) is easy to use, and easy for the customers to put on their bowls as well. There is little to no smell, and the rags do not do the spontaneous combustion thing, though I do not take any chances with that. The wipe on poly and Danish type oil finishes do penetrate a ways and cure and harden. You can build a finish by applying many layers. I prefer this type of finish for non utility type pieces. The Doctor's Woodshop walnut oil has carnuba wax in it, so it can polish a bit.

robo hippy

[Tom Wilson66]

Why not make a drying cabinet in the greenhouse? This would allow the finish to cure outside (no fumes in the house) and be in a warm environment. A few sheets of rigid insulation, an incandescent light bulb and fixture, and some duct tape should provide plenty of warmth for the curing. Be sure to allow for ventilation so the fumes can get out of the enclosure.

[robert baccus]

I would avoid mineral oil under any other finish. The book says that walnut oils are nonreactive also. The ones that do harden I suspect have been altered with hardeners. Also nothing sticks to paraffin. If you are trying to totally soak wood I would think a long soak in mixed tung oil in a container(vinyl bag?) of weeks or longer would work. If you prevent oxygen from reacting it should soak in very deeply and cure later when you have better conditions. The tung oil may satisfy you by it's self for a finish.

[George Overpeck]

Thanks for the thoughts everyone. I guess one of the reasons I had been avoiding the 100% polymerizing oil route was that I suspected it would stiffen up and lock out the next application of oil but going into a bag like Robert suggested would work to save me from having to buy a vat of it. I've messed with BLO just a bit but the yellowing was too much for the birch I'm using, is there a brand that is better in that respect or a way to combat it? If I go with tung oil is there a way to retard it from polymerizing too fast? I've only used Formby's before and it seemed indistinguishable from poly in terms of drying speed and penetration.

[Michelle Rich]

Formby's , so called Tung Oil, isn't tung oil at all...somehow they get to call it that tho...if you want real tung oil, you must find a product with 100% tung oil. I know of no oil that will not yellow/darken birch.

[Reed Gray]

When I am looking for better penetration of a wipe on type poly, I soak the wood with mineral spirits first. It is thinner, and will soak in better than the oil. A lot of oils suggest thinning the mix about 50/50 with solvents. I would guess that it does form a barrier at some point, and keeps the finish from soaking in any more, and this is how you get a surface build. With a really thin piece, full soaking probably isn't a problem. Thicker pieces like you show probably are. I also would think that the solvents would let them penetrate into a walnut oil finish. If the walnut oil was fully cured, maybe not so much. I did see a piece that was put in a pressure pot of finish. It was really heavy.

Walnut oil does not have hardening agents in it. The stuff you buy in the grocery store is not the same as what is used for bowls, and even some oil paints. Because of how it is processed, it will not set up. I am sure additives could be put in to make it set up faster, but to me, that defeats the whole purpose of using the oil in the first place, which is no additives.

robo hippy

[Thomas Canfield]

Temperature and humidity are big factors in drying of finishes. Minimum temperatures and maximum humidity would be what you would need in colder climates. Here in Texas, I have had to put my oil/poly finish pieces inside a drying box (use a light bulb to raise temperature and thereby lowering humidity also) in my 50F minimum shop that will warm up usually into the 70'sF during day, and it still takes a couple of days to get the finish to dry between coats, and longer before final wax. I use a wipe on/off oil/poly mix finish processpicked up visiting Hawaii and they often use a drying chamber because of humidity. A lamp heat (if you can still find the incandescent light bulb) will help to keep the humidity down through the night periods.

[robert baccus]

Michelle is spot on about the Forby's finish. You have no need to worry about the tung oil or BLO polymerizing as long as you exclude oxygen. These hardening oils don't dry--they react with oxygen.

[Bill Boehme]

It seems like woodturners are always wanting to mix all of their favorite finishes together ... I suppose on the assumption that only the best attributes of each will make the combination even better. However, many finishes are not compatible with each other. If mixing things together was a good idea then the manufacturers would already be doing it.

The instructions on all of the film finishes say to make sure that the surface is free of oil and wax -- that sounds like bad news for mineral oil. Mineral oil is a petroleum product that's been in the ground for millions of years without "curing" -- no reason to expect anything different if it is applied to a woodturning.

My preference is to use a single finish product because using too many different finishes together runs the risk of making the wood look drab and lifeless.