Vitriol vs Rubbing Compound for French Polish

[Swifty]

I know it's a fairly obscure art, but has anyone experience with a benzoin - vitriol finish for a French Polish? If so, where does one source the sulphuric acid, and I am a bit unsure of the molarity of the acid. The reference texts I have seen say "dilute 1 in 10 with water", so is that around 2 Mol or should it be less? (I'm thinking more like <1 mol actually). The idea of rubbing my hand in it as required by the technique makes me a bit nervous so I don't want to have it too strong, not being partial to acid burns!

I was particularly interested to know whether this vitriol finish makes the surface more durable or not.

What I have been experimenting with in the meantime is finishing the FP process with an oil rubbing compound I made by adding some talcum powder to paraffin oil and making a slightly abrasive slurry. I rubbed this in and it did make the surface very glossy and removed the fine lines produced by the straightening process parallel to the grain. Unfortunately I did circles also with the rubbing compound and that made very slight swirls - they are not obvious, however, but next time maybe just parallel to the grain also for the compound. The leftover oil was removed using a paper towel slightly dampened with alcohol. The talcum powder is a lot less aggressive that using Tripoli powder or 4F pumice, which tend to rip right through if you're not careful.

Below are some pictures of the trial finishing with the rubbing compound. The best talcum powder as supplied by U-Beaut of course! There were about 15 sessions prior to completion, on a nice piece of sassafras burl. The chatoyance was very reluctant to come out, and only became clear after about ten sessions! The holes in the burl were filled with black TimberMate prior to polishing. I will use this piece eventually in a mantel clock.

[russ57]

Never heard of the technique, but you've certainly brought out the best of that timber.

[China]

I can't comment on the technique although Sulfuric Acid is available at any chemical supplier.

[BobL]

I can't comment on the technique although Sulfuric Acid is available at any chemical supplier.

Maybe you know of some specific suppliers but in general it's not as easy to get as it used to be.
Even its use with lead acid batteries is restricted, eg you can only buy it from places like Supercheapauto if you buy the battery to go with it.

There are a few sites on line that will sell it but being classed as a dangerous good means many will not post it or only courier deliver it locally.

I have bought small amounts from anpros.com.au - you cannot order it on line but have to email or phone through your order.
They only sell pure Analytical grade chemicals so the price is relatively high but I wouldn't suggest using rough H2SO4 for your purposes
Shipping is expensive, my last 500mL bottle of nitric acid (also classes as a dangerous good) cost $50 for the acid and $25 for the postage Melb to Perth plus GST
Sulphuric was a bit cheaper but from memory the shipping was more.

I'd give you some to try but don't have any left and I'm moving to using something less dangerous as I already have too many nasty chemicals in my shed.

[China]

Don't have any issues buy it in Adelaide. I just go and buy it over the counter from my usual chemical supplier.

[Swifty]

Thanks for your comments, I have sourced both H2SO4 (33%) and benzoin now. Guess I will just give it a go! I understand the glaze from the benzoin is quite spectacular, giving the "piano finish" of old.

Incidentally, the famous Sumatran benzoin, "kemenyan" or "damar", I have come across in the wild when I used to work in Sumatra. It's often burned as an incense, has a strong sweet pine resin scent, apparently can also be sensed after it's dissolved in metho. I never kept it, I had a couple of big lumps, now I had to buy it!

[ubeaut]

You could try using the EEE-Eltra Shine with either a 150mm x 75 fold & 150mm x 100 fold Swansdown Mop in a drill.

The mop works with the grain in the wood, so no swirls and will break down the EEE-Ultra Shine from around 1500 to around 20,000+ whilst it continues to cut and polish the surface of the finish. It is fine enough that it will not cut through the surface but will instead make the finish brighter and brighter as worked.

You can finish off with Polish Reviver which will remove any residue of wax left behind from the EEE and make it much harder for shellac to be damaged by water, alcohol and heat. You could also use the talc slurry prior to the Reviver if you really want to go that quarter of a percent further with the cut n polish.

All this is best done a week after the final coat of shellac. This allows the shellac to sink into the surface of the wood and harden. It also lets you see if more shellac applications are needed to finally fill the grain.

Hope this is of some help or information for you.

Sorry for the blatant product mentions.... The devil made me do it.

Cheers - Neil

[Swifty]

Ok, my colleague has provided me with a quantity of battery acid that contains 460 grams of H2SO4 per litre of solution (or around a concentration of 4.7M). Given that pure H2SO4 has a density of 1.83 g/ml, I calculate that to make a 1 litre dilute 1M acid solution, I must weigh out 258 grams of the battery acid and add it to 787 grams (or millilitres) of water. Then I can use this for my vitriol finish! I used grams because I can measure weight a lot more accurately than volume in the workshop. Then I won’t burn my skin if I wash it soon after I do the rubbing.

[jack620]

Then I won’t burn my skin if I wash it soon after I do the rubbing.

Where are you getting that information?

[ubeaut]

Suggest you add the acid to the water and definitely not water to the acid or you may regret it. You could well end up with acid burns burns and/or with holes in your cloths or worse.

Use rubber gloves, eye and clothing protection. Better still don't do it.

[Swifty]

Yes I think “don’t do it” is the best advise. Thank you both.

[truckjohn]

Working with sulfuric acid like this is extremely dangerous and very bad advice. DO NOT DO IT!

Proper vitriol is 95-98% sulfuric acid. It will rot your skin and bones and put you in the hospital.

Battery electrolyte is 12-18% sulfuric acid. Even at this strength, it will gove you serious chemical burns.

Next.. On the application. Sulfuric acid is extremely good at DISSOLVING wood fiber. It's how they digest wood for paper pulp. Put it on your furniture and it will dissolve that too.

Next.... Sulfuric acid dissolves all sorts of impurities, like iron and nickel, into a clear solution, and they don't show up till you neutralize it... Then all that muck leaves multi-colored stains etched into your surfaces. Yay.

Once again, The Internet is full of bad advice. Leave off this before you get seriously injured.

[Swifty]

So I went ahead with a benzoin glaze trial, I spirited off rather than using the 1M sulphuric acid. I have abandoned that idea, although I can't help wondering how the old master piano finishers managed to do the vitriol glaze and yet not get burnt. That is in the literature, from more than one source, not from the "internet", but thanks for the warnings.

In this case I French polished a piece of Tasmanian myrtle, beginning with a pore-filling exercise using 4F pumice, which produced a lovely flat surface. Then there were nine sessions of bodying up over a period of about two weeks, producing an acceptable (I think!) finish. I noticed that the myrtle only started to exhibit some chatoyance after the sixth session. After that it just improved, bringing out bird's eye textures that were hardly visible before the FP.

There is so much to still learn...

Anyway, you can see some lumps of the benzoin a.k.a. Sumatran damar, in the photos below. SWMBO bought this in Java last month while she was there, it cost $3 per kilo, quite a bargain, the 2 kg will last me forever. I dissolved a small amount in alcohol at 1:9. I had to use a fair bit of paraffin oil on the special benzoin rubber to avoid burning the FP below. All went well and I laid down a coating of the benzoin glaze. Then I first tried to remove the oil with naphtha - ughhh, don't ever do that again! Way too harsh. So redid the benzoin glaze and just removed by spiriting off with alcohol-damped paper towels, that seemed to work.

The resulting surface is indeed brighter than the FP alone, giving a near piano finish. I still need more practice to remove some lines parallel to the grain that are visible in the glaze. The conclusion from the trials, is that the benzoin glaze did give a slightly superior gloss / mirror finish, but FP alone isn't bad either! I can't wait to try it out on my next clock projects. But I am concerned with how soft the benzoin might be...

Cheers
Swifty

[truckjohn]

Ok, so I read a bit about this... They reacted sulfuric acid, acetic acid, tannic acid and iron to form the black pigment used in many wood finishes. That makes sense, but making your own is unnecessary now due to quality, color fast pigments available.

They didn't put sulfuric acid on the bare wood or wipe it with their hands.

On old finishes.. They had to be quite soft due to no climate control indoors. Spring and fall brought condensation while heating during the cold of winter brought bone dry single digit humidity. Finishes had to be very soft so they wouldn't crack to pieces and peel off. Think of spar varnish used on outdoor things. It's mushy, but it doesn't crack when the rain comes.

Now, we have air conditioning, winter humidification, and high quality urethane varnishes that apply reliably and brush very well.