Restoring a Petzval Brass Sleeve

[Steven Tribe]

There is always the problem of originality. When does the current finish become unacceptable?

For me, there was no dilemma in deciding to redo this one.

It is a Gasc & Charconnet with US agent George Bryant of Boston. It was sold on Ebay sometime earlier this year (US) and then relisted by a Vietnam seller about a month ago.

It was not very pretty, but the glass is basically good.

I would like to show how the appearance (and function) of the sleeve can be improved. Mostly brass finishing, but also renewal of the two velvet seals/bearings and, perhaps, fitting a new tangential drive.

Just started to-day. So all I can show is the horrible lacquer (opaque, streaky and over pigmented!) and some basic removal with 400 wet paper of the worst areas. And a shot of the inside edge showing one of the missing velvet seals.

[Steven Tribe]

Well that went quite well! All the apparent scratches were in the lacquer. The first shows after completion with 400 and 800 grade on the outer edge (approximately 1").

No matter how fine the grade, the brass surface finish is very unforgiving for any surface polishing which is not at exactly at right-angles to the barrel sleeve. I find the most secure way to do this is to rotate the item whilst holding the paper/cloth at rest.

The original finish on brass lenses does vary quite a lot. Some retained quite a lot of evidence if brass turning, whilst others removed all evidence of working processes. It is quite possible to produce a brass finish which is well above the original standard. This is terribly common in the vintage car "business" where "user cars" like Pre-war Fords are given a chrome and paint finish that exceeds even Rolls-Royce's standards!

This Bryant engraving is quite fun. Generally, engravings are very conservative and timeless. The ribbons/scroll are very similar to the decorations found on pre-printed C de Vs from the same era. In fact, there are articles giving the changes in style of C de V cards along with date periods. A pity that engravings give few clues as to dates.

A section on lacquer must wait a few days as I have been less than satisfied about the methods I have used until and will experiment with a modified air brush system.

[Tin Can]

Very interesting, thanks for showing your process.

[Steven Tribe]

While I had permission to use the kitchen I did the lens hood too. This has been brush painted black on the outside for no apparent reason. Results are as shown. The usual join, which is part of the early manufacturing of brass tubing, is quite easy to see in the first photo. It is the purple streak about 1/3 of way up from the bottom. The most common join is only slightly noticeable as a line with a slight indentation and slightly more prone to corrosion. I think a different system has used with the thinner brass used on early style brass lens hoods. Does anyone know the process involved?

[Jim C.]

I've cleaned one of my Petzvals and have noticed the same join line, I believe that the hood was slip rolled then
the ends were either soldered or brazed, the heat from soldering or brazing would account for the slight discoloration.

[Steven Tribe]

I think the different coloured metal is a sign of solder and the varying thickness of the band must be due to two oblique edges being joined and further surface working over the overlap brings out the inperfections of the edges.

Here are the completed velvet seals - I did another Petzval at the same time. This degradation of seals or complete absence is often overlooked. Could be due to nervousness about removing the 4 (sometimes just 2) screws holding the gear housing! A rattling barrel in a brass sleeve will give additional wear or failure for the mechanism.

[Jim C.]

Did you use velvet fabric and cut strips or velvet ribbon ?

[goamules]

You are becoming a good restorer, perhaps the best!

[Steven Tribe]

Did you use velvet fabric and cut strips or velvet ribbon ?

I gave up trying to cut velvet years ago. One of my daughters has sewing and dressmaking experience and pointed me towards standard velvet ribbon. It doesn't quite have the density of 19th century velvet and is very slightly thicker - but works as long as both edges are securely glued down.

[Steven Tribe]

Ever wondered what holds the delicate brass turning knob onto the axel with the gear?

Well appears to be just a heat seal! That is, when the knob is heated it can be forced off the axel. And replacement is the reverse (in theory) - heat the brass knob again, push on and the contraction of the brass will grip the steel.

I needed a replacement drive for the G & C which had disappeared. No luck in the WTB section so I needed to lengthen the double ended one I had from a smaller diameter magic lantern lens. The length of the hole in the brass knob allows at least an extension of more than the 1cm I needed to allow air between the knob edge and the brass sleeve.

This very much cosmetic finish. The replaced velvet provides a secure friction between the lens barrel and the brass sleeve and I don't think anyone uses it for focussing.

The lengthened axel is to the right.

[Tin Can]

Interference fit

[Steven Tribe]

The metal stock I used for the "gearbox" was a very large bearing of about the same radius of the sleeve it has to be attached to. A "no name" alloy of copper, but close to brass appearance when polished and much softer than brass to work. No magic metal working here, just angle grinder and files.

I couldn't make a square cut out for the gear, but a drilled hole doesn't compromise strength.

The body thickness has to be very precise if you are reusing the original screws. They can quickly too short or long to bed in the shallow sleeve threads.

[Jim C.]

The "no name " alloy is bronze, which is copper and tin.
Be aware that there are sintered bronze bearings and oilite bronze bearings, both are powder bronze compressed,
oilite bearings add a lubricant to the sintering process. I don't think a sintered material would have much strength.

[Steven Tribe]

I know the basic content of bronze bearings, but the actual proportions of tin/copper and many other additive metals vary a lot, like the colour. I assumed some were poisonous so took every precaution. This came from an old breakers yard in a fishing port so probably made in the good old way.

[Jim C.]

I know the basic content of bronze bearings, but the actual proportions of tin/copper and many other additive metals vary a lot, like the colour. I assumed some were poisonous so took every precaution. This came from an old breakers yard in a fishing port so probably made in the good old way.

Very true, another thought is that what you used may not have been bronze but leaded brass,
it machines exceptionally well because of the addition of lead.

[Steven Tribe]

The lacquer job must wait a little but the new geared wheel is finished.
As the steel axel only fits about 5mm into the brass knob - longer in would make the knob touch the sleeve - I decided to "improve" the fit.

The steel rod is quite soft metal so I made few lateral impressions on the end which goes into the hole. The used solder to fill up the hole and insert the hot axel. I have no illusions about a good solder bond to the steel, but the presence of solder in the new grooves makes it firm enough to move the lens back and forwards.

The remaining brass knob will be a useful spare part which can easily be provided with a thread.

[Steven Tribe]

I have come to the conclusion that I need to renew the 4 small threads in the sleeve that take the 4 screws. Not only do I not have a complete set of 4 screws which match in appearance, but they don't fit very well in the threeds. The existing thread holes are something under 3mm (French, Napolean, metric) so I have cut 4 new 3mm threads. Now to find suitable brass screws.

The top is a newly cut thread compared with the "uncut" 3 others.

[Steven Tribe]

I found 4 matching head 3mm brass screws by looking through a drawer with old electrical fitments. A bit of "lathe work" - using an electric drill to clean off the chrome finish - produced a more vintage finish.

The orange tint is a fake, I used a filter, or rather, a coloured lamp screen.

Shellac flakes have been purchased. As of to-day, I am still fighting cloudy solutions. I think the quantity of wax in shellac dissolved in ethanol/methanol is important?

[coisasdavida]

Banana extract instead of shellac?

[Steven Tribe]

I think I will continue with the shellac idea for the time being.

Meanwhile, I couldn't resist a "you know where I found it" large Derogy Petzval needing work.

This had been modified for easy studio use with a removed brass hood and a discarded R&P mechanisms. It is also covered with the light wispy growth which is (usually) easy to clean off - one of the advantages of pre-Preussian glass. These "problems" and the apparent shorter length (just 17.5cm instead of 21cm) meant it was quite reasonable in price. The thread at the front which held the brass hood has been removed in a lathe at some time past, but can just be seen.

The job here is a new R&P mechanism and a replacement hood. The finish has just the right sort of patina condition which is almost perfect!

[Steven Tribe]

The hoodless Derogy arrived from France yesterday.

A not uncommon case of inadequate description. "Fungus", as expected turned out to absolutely nothing. The only damage I have seen in uncoated glass has been insignificant "bloomlike" patches.

It turns out that efl is not 250mm, but a huge 350mm, which makes it something between a Dallmeyer 3a and a 5d. Very Fortunate, as I have too many 10" and f3.

I still have a aged store of brass and, in this case, I found a couple of brass turned items which could serve as replacement hoods. These have a thicker base, whilst the tube has been turned up on a lathe which makes for a thinner and more like the original (early brass petzval hoods, anyway) tube.

There has been some discussion elsewhere about cutting thin metal. I used a thin (1mm) cutting disc on an angle grinder for the tube.

As the thread on the front lens cell has already be removed, apart from the last two turns, I decided to make a push-on fit. Trying to fit on the remaining thread would have made it difficult to remove again without unscrewing the achromat cell from the barrel.

materials and results are shown below.