Polyurethane vs Lacquer vs Shellac

[DelF]

Hi Dave

 

This is the one I use. It's very pale and leaves a lovely warm sheen:

Liberon is a great brand for all sorts of wood care products.

 

Derek

[Jaager]

22 minutes ago, DelF said:

Liberon is a great brand

An old wood finishing book had instructions for French polish.  The instructions were to use a cloth pad that had a small quantity of Linseed oil in the middle which was then soaked with shellac.   The pad was to be rubbed on the wood surface with constant movement and a jet takeoff removal.  Otherwise the cloth will leave its weave pattern on the finish - which was to be only a wet layer.

 

I took this to mean that French polish is primarily shellac with a small admixture of polymerizing oil.   It seems to me that Tung oil could be used instead of Linseed oil. 

[DaveBaxt]

Thansk for the Heads up regarding French Polish Liberon. How to apply this. Cheers.

 

[wefalck]

I made several pieces of furniture with a simplified version of French Polish, using modern materials. Traditional French Polish would consist of rubbing a mixture of very dilute shellac solution and pumice into the pores of the wood in several sessions. I replaced this with organic solvent-based sanding filler, rubbing down the surface with steel-wool. For the actual polish I used a commercial german brand of shellac solution (Clou which is equivalent to Liberon, but somewhat cheaper).

 

The application pad ('tampon') was made from a worn-out flannel pyjama that was stuffed with cotton wool. The trick is to have the pad well-soaked in the middle, but not trickling and then to apply parallel strokes in a jet landing and take-off movement (as noted above).

 

Do not stop, or the pad will stick to the surface and leave fibres in the coating. If this happens, let it dry and and go over it with fine steel-wool. Also, if one works too wet and stays too long with the pad on the surface, the already applied coats will soften, resulting in an uneven surface.

 

If something goes wrong, you can always rub down the surface with steel-wool and begin again.

 

Having said that, on models I would not use French Polish, unless it was a model of a yacht. I would rather use a commercial solvent-based sanding filler or shellac and rub the surface down with fine steel-wool. Real French Polish just gleams too much for models. I reserve this for display cases.

[Dr PR]

Jaager,

 

Good points. We used 100% ethanol in the lab and had to keep that tightly sealed.

 

In an open container of an ethanol-water mixture the ethanol will evaporate faster than water, so the concentration of ethanol decreases (the water concentration increases). Of course some water will evaporate also, especially in low atmospheric humidity conditions.

 

I wonder if the residue (translucent gel) that you mentioned is oxidized shellac?

[Jaager]

15 minutes ago, Dr PR said:

I wonder if the residue (translucent gel) that you mentioned is oxidized shellac?

That was my first thought, but a comment here has me questioning that.  If shellac in flake form is subject to oxidation, then a shellac finish that is 200 years old should also be subject to it?

I would think adsorbing water into the flakes could be it, but then there is still the situation of why a shellac finish does not also adsorb water.  Or perhaps it does but the concentration of atmospheric water is too low to affect a flat surface.  Maybe the flakes have a higher surface to volume ratio?  Maybe the flakes can absorb water?

 

As for ethanol : water   the description of azeotrope for that mixture should explain why it is a very specific situation.

[wefalck]

I am not sure, what you mean by 'oxidised' shellac? Schellac does not oxidise to my knowledge ...

 

Pure (96%) alcohol is the normal solvent for shellac (flakes). You can make any mixtures you want. For instance, I keep a small quantity of shellac with a thick honey-like consistency as glue. Otherwise you can dilute it to any consistency you like/need with alcohol.

 

[DaveBaxt]

I apologise if it apears I have hyjacked this thread in anyway but can anyone confirm that ethenol is also known as denatured alcohol or here in the uk is called ordinary methylated spirits used in camping stoves?  Is this also what is used when thinning and removing shellac and also what is added to the shellac flakes ? Best regards Dave

 

[wefalck]

Yes, methylated spirit is denatured alcohol as useg e.g. in rechauds, camping stoves etc. and can be used to make shellac solutions.

[RossR]

No need to apologize.  In some parts of the US Ethanol can be purchase at 95% purity, for human consumption, usually under the brand name Everclear.  This is often used for thinning shellac or dissolving shellac flakes.  Denatured alcohol is ethanol that has additives to discourage people from drinking it.  Where I live I can only get denatured alcohol and use that for thinning and mixing with shellac flakes.  

[DaveBaxt]

Thanks guys. Here in the Uk we can get Ethernol at 95% but calls it denatured ethernol and not methylated spirits and is more expensive. I understand that the other 5% is Methenol but unsure if there is any difference. In the Uk we are unable to buy higher than 95% ethernol and wonder if this makes any difference when using Methylated spirit rather than 100% ethernol when mixing with shellac? 

[RossR]

I get good results with denatured alcohol.

 

[DaveBaxt]

58 minutes ago, RossR said:

I get good results with denatured alcohol.

 

Thank you Ross

[Jaager]

4 hours ago, DaveBaxt said:

In the Uk we are unable to buy higher than 95% ethernol and wonder if this makes any difference when using Methylated spirit rather than 100% ethernol when mixing with shellac?

The reason for mentioning the ethanol:water azeotrope is to point out that it is essentially impossible to have ethanol that is stronger than 95%.  Even if you started with an expensive lab reagent bottle of 100% ethanol, unless you used it in a sealed chamber with an atmosphere free of water vapor, the 100% ethanol would quickly return to 95% by extracting water from its atmosphere.

 

In the US, there is a significant Federal tax on drinking alcohol ( not as significant as it once was, because it is a fixed amount instead of a percentage of the alcohol value ).  If a poison is added to the ethanol to make it unsuited to ingest, there is no tax.  The common term for this is 'denatured' and its whole purpose is to avoid the tax.   Long ago, I think methanol was the additive.  Now I think the additive is an emetic agent. 

 

There used to be methanol available.  It is available as 100%.  The danger in using it is probably not worth any advantage.  The vapors can be inhaled and while ethanol is metabolized to acetaldehyde  and then acetic acid,  methanol goes to formaldehyde and formic acid - you don't want it.  Methanol also evaporates more quickly than ethanol.  This is not an advantage during application of shellac.  I had an idea that ~100% isopropanol (which is available, but is expensive)  would have a longer application time and not have the 5% water.  I do not think that the length of any additional time is practically significant.  The 5% water in ethanol is as the azeotrope.  That is a special state of water. Whatever straight water might do to shellac, the water in the azeotrope is not able to do it.  That water is owned by the ethanol.

[wefalck]

You cannot technically make ethanol at more than 96% at normal atmospheric conditions because it becomes hygroscopic and dilutes itself when left standing open. Many countries levvy a heavy tax on alcohol fit for human consumption, which is why such ethanol is expensive, though the production is very cheap.

 

Methanol is another alcohol, but it is not fit for human consumption, it is rather detrimental to the health and can result e.g. in blindness or even death. For this reason ethanol is 'denatured' with methanol or other substances to make it unfit for human consumption and to give it an unpleasant taste and smell. It is added to a level of a few percent. This, however, does not change its technical nature and it remains a good solvent for shellac.

 

If you live in a country without a heavy alcohol tax, it may be more pleasant to use the 96% ethanol, rather than methylated spirit.

 

Blindness used to be an occupational hazard among 'french polishers' as cheap alcohols were used, where the distillation process was not carefully controlled to separate ethanol from methanol - the guys would take a sip from the bottle between using it to make their shellac solutions ...

 

P.S. Jaager was a bit faster with his post ...

 

Edited January 2, 2023 by wefalck

[Dr PR]

Jaager,

 

I checked a can of Denatured Alcohol fuel I have for cleaning 3D resin prints. It contains ethanol and methanol, but the can doesn't give the concentrations. So they are still using methanol to denature ethanol and make it unfit for human consumption.

[DaveBaxt]

8 hours ago, Jaager said:

The reason for mentioning the ethanol:water azeotrope is to point out that it is essentially impossible to have ethanol that is stronger than 95%.  Even if you started with an expensive lab reagent bottle of 100% ethanol, unless you used it in a sealed chamber with an atmosphere free of water vapor, the 100% ethanol would quickly return to 95% by extracting water from its atmosphere.

 

In the US, there is a significant Federal tax on drinking alcohol ( not as significant as it once was, because it is a fixed amount instead of a percentage of the alcohol value ).  If a poison is added to the ethanol to make it unsuited to ingest, there is no tax.  The common term for this is 'denatured' and its whole purpose is to avoid the tax.   Long ago, I think methanol was the additive.  Now I think the additive is an emetic agent. 

 

There used to be methanol available.  It is available as 100%.  The danger in using it is probably not worth any advantage.  The vapors can be inhaled and while ethanol is metabolized to acetaldehyde  and then acetic acid,  methanol goes to formaldehyde and formic acid - you don't want it.  Methanol also evaporates more quickly than ethanol.  This is not an advantage during application of shellac.  I had an idea that ~100% isopropanol (which is available, but is expensive)  would have a longer application time and not have the 5% water.  I do not think that the length of any additional time is practically significant.  The 5% water in ethanol is as the azeotrope.  That is a special state of water. Whatever straight water might do to shellac, the water in the azeotrope is not able to do it.  That water is owned by the ethanol.

Thanks for clearing that up and what is a very in depth insight into ethernol. Best regards Dave

[DaveBaxt]

8 hours ago, wefalck said:

You cannot technically make ethanol at more than 96% at normal atmospheric conditions because it becomes hygroscopic and dilutes itself when left standing open. Many countries levvy a heavy tax on alcohol fit for human consumption, which is why such ethanol is expensive, though the production is very cheap.

 

Methanol is another alcohol, but it is not fit for human consumption, it is rather detrimental to the health and can result e.g. in blindness or even death. For this reason ethanol is 'denatured' with methanol or other substances to make it unfit for human consumption and to give it an unpleasant taste and smell. It is added to a level of a few percent. This, however, does not change its technical nature and it remains a good solvent for shellac.

 

If you live in a country without a heavy alcohol tax, it may be more pleasant to use the 96% ethanol, rather than methylated spirit.

 

Blindness used to be an occupational hazard among 'french polishers' as cheap alcohols were used, where the distillation process was not carefully controlled to separate ethanol from methanol - the guys would take a sip from the bottle between using it to make their shellac solutions ...

 

P.S. Jaager was a bit faster with his post ...

 

Thanks for explaining that to me which has made me understand the difference between Methylated spirits and ethernol. So if I purchace clear Methelated spirits without the dye, It will  still have the methanol in it ,hence why it is called methelated spirits? Ethenol does seem to be more expensive so perhaps has the tax on it.

Edited January 3, 2023 by DaveBaxt