BIG prop and a huge mistery - PLEASE HELP!!!

[pmdec]

Hi Adrian,

Preserve old props is very difficult. In the field of aviation, people tend to put everything constantly new. The result is old props sandpapered (even "Kärcherized") and bright from epoxy varnish... Even in museums. What a pity!

So, what to do?
First, I agree with you not to use oil: it is too risky it will unstick a decaying varnish.

From some times, I thank to use shellac to preserve props. I have bought some different kinds (see below) of flakes. I tried different recipes on old piece of wood and it seems perfect, but using it on prop which have their decals makes me dubious... ... So, for now, I have do nothing as I am afraid to make some mistake.

I have some questions about shellac, and the first one is what are you talking about: is it this very one http://en.wikipedia.org/wiki/Shellac ?
Or synthetic ?

The first (the true) one seems to be sold in France as "gomme laque", which comes with many kinds and colors. The two main kinds are:
- natural (contains wax): the flakes are a little flexible,
- wax free: flakes are brittle (I'm not sure of the word).
And both are coming in many colors from light yellow to dark brown. Which one are you using?

Second question: which solvent? Alcohol? Ethylic? Isopropylic? Pure? 95°? 90°? Less? And how much flakes?

Third question: how to use it? With a brush, or by using traditional French Polish method?

And the last question, which should to be the number zero: before shellac, what do to for not sealing the dust inside the small cracks of the old varnish? Soft dry brush? Water seems "forbidden' as it will impregnate and discolor the wood? Alcohol?

So ... I understand I am asking for a complete (and free) preservation course! But i'ts all for the sake of old props!

Regards,
PM

[oinkitt]

Finish Conservation

Hi PM,

Thanks for the email, I will try and answer all your questions.

An original finish should never be removed from any item. The problem is that most people don’t understand this and proceed to remove it either chemically or mechanically. I have to be honest, when I got my first antique set of drawers 30 years ago I took it home, got my belt sander out, well you know the result. Half way through I learnt about patina, and sold the drawers unfinished. When I look back I think, sure I wrecked those drawers, but it was nothing of importance and learning that lesson saved all the real important furniture I got from that point.

As it says in the link in your post – wax and oil finishes went out when shellac finishes were devised in the 1700s. These finishes are extremely labour intensive to do, and chances are you will never come across one. I never have.

Thank you for bringing up the point re the decals. One should generally never coat decals or paper items with any lacquer product. I would carefully go around the decal with a small artists brush. Remember the thin shellac will bleed from your edge so don’t load the brush too much. If you don’t know what to do – DO NOTHING!!!!Think about it for a while, experiment on a similar scrap piece of wood. There is plenty of time to do something in the future. I have just finished a model boat I left for 4 years because I wasn’t sure what to do with it.

I use the products that are in your link.

http://en.wikipedia.org/wiki/Shellac

I generally use red button shellac or brown flakes. Choose the colour depending on the finish you are trying to create or recreate. All of the flake or button shellac is dewaxed and easy to use. I NEVER USE POLYURATHANE UNLESS DOING MODERN WORK.
Shellac can also be coloured with natural pigments to match any finish. These pigments are in powder form and come in an amazing colour range however browns and black are the main ones most people use. Remember when using pigments – a little goes a long way. Is better to slowly build up the colour coat by coat, you generally can’t mix in lots of pigment and build the colour up quick. My prop was the exception to that rule. Remember each finish is unique.

The best solvent to use is denatured alcohol as it has no water in it so it evaporates quickly, it’s a little hard to get so most people use methalated spirits which is nearly as good.

It’s hard to tell you how much flake to add to the liquid. I make 5 litres at a time. I make a pretty thick mix, when I use it I add liquid to thin it if necessary. A thin mix is little thicker than water, say 25% shellac, 75% metho/alcohol.

To apply the finish over an existing finish I generally use a very soft brush. I use depurfumed skunk hair brushes.

To remove dust us a soft brush or low pressure compressed air. Don’t use alcohol or metho it will remove the existing finish. A damp cloth can be used if the finish is reasonably smooth.

I hope this has answered you questions.


Regards,


Adrian.

[oinkitt]

Adrian,

Thank you very much for your help!
I've applied the shellac in one thin coat and this huge chunk of wood looks magnificent now! I will send you photos soon. I'm not so sure about putting on the wax anymore....? It looks so good right now and most of the uneven spots, water marks, etc. are pretty much blended.

The one coat brought this thing back to life!

Thanks much!
David

Hi David,

Good to hear you are happy with the results.

I generally find a shellac finish is too shiny. By adding a wax finish on top of the shellac you get a low sheen shine.

Regards,

Adrian.

[oinkitt]

Finishes

Here are some pictures of the boat I talk about in my reply to PM

As you can see it was in very poor condition when I got it, just a painted hull, no deck and all the fittings missing.

Most people dont believe me when I tell them it is not the original finish.

You can make a new finish look old it just takes allot of time and experience.



Regards,



Adrian.

[pmdec]

Hi Adrian,

Thanks a lot for all these details. Your boat looks very very fine!

Regards,
PM

[Dave]

Adrian, thanks for your comments. I have taken the liberty of pasting them into the closed thread titled "Don't restore your prop", as I think it's particularly relevant to that discussion.

[pmdec]

Hi Dave,

As some people reading this forum are not from USA nor Australia, it seems necessary to be cautious using "denaturated alcohol" : in Europe, denaturated alcohol has very different formulas according to the country it is sold. Read this : http://www.distill.com/specs/EU2.html
In France and in United Kingdom, standard denaturated alcohol contains water for about 10%.
In France, the bottles marked "Alcool à 95°" are, in fact, denaturated alcohol with 10% water, as "°" are calculated in volume and "%" in mass. The difference came from a physical property: when you mix 1 liter of water and 1 liter of alcohol, you don't have 2 liters but only about 1.9 liter.

So, to make a good shellac, you have to buy in France "Alcool à vernir 99° " (English word for word "Alcohol for varnish 99°") which is 5 to 10 times the price of standard denaturated. But with "95°", it don't evaporate quickly enough, and with "90°", there is so much water the shellac goes whitish.

I don't know what you have to buy in United Kingdom. In France, if you live in the South-West or in the North, it seems you can buy good denaturated alcohol in Spain or in Belgium.

Regards,
PM

[Dave]

Thanks, Pierre.

I just realized that I can COPY posts into another thread (and they also remain here in this thread), so I've also copied your post above into the closed thread started by Bob some time ago titled "Don't Restore Your Prop"

This is a very useful discussion and should be archived as a "sticky" at the top of the list. I plan to also link the thread to the Wooden Propeller web site for reference.

Thank you both for sharing this very useful and relevant information!

Dave