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Old 09-27-2008, 12:59 PM   #1
Bob Gardner
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Default Don't restore your prop !!!!!!!!!!!!!!!!!!!!

Forumites might wish to note that if you restore your vintage prop you are very likely to reduce its value, both in terms of money and also its value as a historical item.

If you intend to sell your prop, leave it exactly as it is. Don't even clean it.

If you intend to keep it and really really want to clean it, do so very carefully and sympathetically with gentle materials, then wax it with pure beeswax polish.

If the fabric is hanging off and there are splits in the wood, find an expert who can carefully conserve the prop. This means halting the decay of the prop without causing damage. It does not include repairing previous damage which is a valid and acceptable part of the life of the prop.

Don't clean it with harsh materials such as petrol, meths or sandpaper. Don't paint it. Don't restore it unless it is completely derelict.

One way of protecting your prop from your desire to restore it, is to put off the process for a day at a time until the urge to restore goes away. Always bear in mind that an unrestored prop can always be restored in the future but a restored one can never be returned to its original condition.

With regards to everyone,

Bob
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Last edited by Bob Gardner; 06-22-2011 at 04:59 AM.
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Old 01-24-2009, 06:38 PM   #2
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Default Propeller Conservation

When I bought my prop the previous owner had cleaned around the hub - I presume this was in order to read the markings. As this post suggests this should NEVER be done. I would have suggested the person do a "rubbing" with pencil and paper. You should never do anything that can not be reversed.
Thanks to my 30 years of experience with timber, and timber finishing, I was able to recreate the original finish.
The first 2 pictures are of the prop the way I got it. The second picture is after conservation.
This was achieved by mixing a thick batch of shellac and mixing in brown umber (pigment). It was applied to the required area and treated (fried) while still wet with a gas blow torch. Several coats were required but the repaired areas are not detectable.
This is probably something that should be left to someone with considerable expertise.
Any attempts to recreate a finish should be done on test pieces until it is perfected - generally every finish is different and due to mixing, application, and the conditions it has lived in
Remember if in doubt - DONT DO ANYTHING.
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Old 01-26-2009, 03:05 PM   #3
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Nice job! What kind of prop is it? Can you add a picture of the whole thing?
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Old 01-26-2009, 06:35 PM   #4
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I agree. Nice job! Nice job on the prop and on the narrative above explaining it. I like the way you said "Unless you're an expert, DON'T DO THIS AT HOME".
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Old 02-07-2009, 07:00 AM   #5
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Default Prop Conservation

Thanks to both moderators for their praise. The repair job actually looks beter in the "wood" so to speak. The prop is an Arvo 504 - I think Dave identified it for me some time ago. I will add a picture for the forum but I am having trouble getting a good photo because of the window above it. I will block the window up in the near future and see how that works.
 
Old 03-05-2011, 09:07 AM   #6
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Default ADDED - Adrian's (oinkitt) post

I have copied and pasted Adrians comments from another thread, even though this present thread is closed for additional posts (moderator privilege). Please read the original thread to put these statements in context and thanks, Adrian, for the additional comments.

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.
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Old 03-05-2011, 09:18 PM   #7
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(Copied from this thread by moderator)



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.

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Old 12-06-2011, 11:52 AM   #8
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Although this thread is "closed" (to reduce "clutter"), we welcome additional information on a selective basis. Please PM or email me if you have factual information that you feel should be included.
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Old 12-06-2011, 12:02 PM   #9
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Shellac

I had an interesting discussion with the owner of shellac.net today. He has 40 years of experience in the use of shellac, and his website contains a lot of useful and relevant information to be considered in those rare cases where refinishing a propeller may be indicated.

A few points of our discussion:

1. Prior to 1920 (when the nitrocellulose finishes were developed) shellac was THE clear sealant and sometime finish of choice. It stands to reason that it is therefore present as a base coat on virtually all WW1 era propellers.

2. Un-waxed shellac can create a good bond between almost any 2 other finishes, so that a previously varnished item can be coated with non-waxed shellac, and vice-versa.

3. Shellac needs to be thinned with denatured alcohol, and only 190 proof or greater versions should be used. It should be applied in thin coats and not by brushing back and forth, with light sanding in between coats.

4. It can be colored and mixed with various pigments as noted in posts above.

If a prop absolutely MUST be refinished, I would highly recommend reviewing the information on the link aboce.
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Old 03-02-2011, 10:05 PM   #10
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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
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