Finish sequence

[shipman]

Here's a question:-

 

I intend building a series of miniature oared boats.

The wood will be Pear, assembled with PVA.

 

The simplest approach would be to complete them and finish them with Tung oil.

 

But I'd like to introduce a little colour to several strakes and fittings, probably using washes of thinned Tamiya acrylics, with the remainder wiped with Tung oil.

 

What would be the best sequence; to paint and complete the model, then ad the oil?

 

My intention is to use the colour sparingly, attempting to get a used appearance.

 

Any thoughts would be welcome.

[Charter33]

My initial thoughts would be that the tung oil might cause adhesion problems with the acrylic paint if the oil went on first. The paint will penetrate the bare wood better, but might bleed from the strakes and fittings into the surrounding material. From a practical perspective, I'd say this is a perfect example where a few test pieces trying the alternatives would be time well spent before getting anywhere near a model. 

Another thought though - any mileage in applying the oil to those areas to be unpainted first to seal them and then add the paint, then apply the oil over the paint once dried?

Sounds like a very interesting project and I look forward to seeing how it goes.

Good luck!

Graham

[davec]

Agree that some testing would be in order.  As long as the paint adheres over the clear finish, would think about applying the clear first.  Seems like sealing the wood would make it less likely that the thinned paint will soak into wood in places beyond where you brush it.

[shipman]

Thanks for your advice, Graham and Davec.

 

I feel you are both correct; experimental testing is the sensible approach here.

Will be happy to share results, along with a build log.

 

Itching to get started, yet waiting for the kits to arrive from 'Falconet'.

Edited November 10 by shipman
removal of rogue word!

[wefalck]

I haver never used tung oil, but understand that is an oxidising one (like lineseed oil). As the colleague said before, acrylics don’t like oily surfaces. So, there two options: either use oil-based paint, or use shellac or a sanding sealer instead of the tung oil. The latter two are compatible with acrylics.

[shipman]

Thank you, Eberhard, I'll take your advice on board.

 

I understand 'Blue Ensign' has had success on his Longboat models using acrylics for colour in combination with 'wipe on polly' (W O P).

What is this 'W O P'?

[wefalck]

A polyurethane formulation, I suppose, that is not brushed on, but wiped with a cloth, as was traditionally done for shellac.

[shipman]

Another thought....

 

why not use slightly thinned PVA as a wood sealer?

[wefalck]

Because you really want something with less surface tension and something that is neither water- nor oil-repellent.

 

Shellac is made up with alcohol and alcohol has a much lower surface tension than water. The same applies to nitrocellulose-based wood-sealers that use some organic solvent. The latter work better with more resinous woods, as the solvent attacks the resins, while a water-based acrylic sealer would be repelled.

 

The effect of oxidising oils or shellac is that they fill the pores and act quasi like optical fibres: the incoming light is guided deeper into the wood pores and absorbed deeper in the wood. This is why wet wood or treated wood looks darker. On dry or untreated wood, the light is reflected already at the pore entrance, which is why it looks lighter.

 

So for a good deep glow of the wood, you want something that penetrates deep into the wood and fills the pores.

 

[shipman]

Once again, thank you Eberhard.

 

I know you are fond of using shellac; so do you dissolve flakes of the stuff in alcohol (IPA?)

And by what proportions?

Once prepared, how long will it keep in a sealed screw-top mini jar?

Using the same ingredients in the same proportions, will that result in the same colour?

 

Thanks for the tips......I've never used shellac.

[wefalck]

The colour will depend on the kind of shellac used, there are orangee to almost white variations and the number of coats.

I keep small amounts in old film-jars (wisely collected them over the decades ...) and they keep for years. I make different dilutions for different purposes. The good thing is, that you can just add more alcohol to dilute the solutions again. You can actually use denatured alcohol, if you don't mind the smell.

Some of the nicest surfaces result, when you rub the shellac treated surface (after a good drying period) with very fine steel-wool (0000) and then polish it up again with felt-wheel in the hand-held drill.

Edited November 12 by wefalck

[Thukydides]

I will just add on the acrylic question, if you are using an oil based sealer you can paint acrylic over it, but you probably need to abrade the surface a bit and use some sort of miniature painting primer (e.g. Vallejo) or it will flake off.

[Keith Black]

 One can paint over polyurethane using acrylics. It's easy to get outside the line when working at small scales, when painting on top of polyurethane it's very easy to remove that area of paint where a mistake occurred.