Yecch!!!, opening a Perkin and Rayment Optimus

**snuck** · 11-Oct-2006, 19:51

Well it arrived in the mail much to my delight, so I set about trying to clean it up. It' a cannon at 3 1/4 inchs wide, and over 4 inche long.Thankfully the ebay picture was interpreted correctly, and despite it's orrible' looking pic, the glass elements cleaned up to almost perfectly! There is nary a microbubble in this lens (to think that they once claimed that bubbles made your pics better....

I found one glued element up front, and an air spaced element on back. Petzval if I'm not mistaken.... very, very happy. After cleaning up the lens elements, I set about cleaning up the mechanism. Years of sitting on the shelf had taken their toll. much to my suprise, after dousing off the focus mechanism and aperture with ronsonol, the black coating on the interior started coming off with a rub of my cloth! Much to my horror, it appears that they used some kind of sooty candlewax to darken the interior of the brass lens at the turn of the previous century. Now I have to clean out all of this crud and respray the interior with matte black!. Ah well, at least I'm happy. I'll post pics later.

Course I should actually take a picture with the lens first before crowing about it!

**Joseph O'Neil** · 12-Oct-2006, 05:47

Originally Posted by snuck

Much to my horror, it appears that they used some kind of sooty candlewax to darken the interior of the brass lens at the turn of the previous century.

-snip-

Yepper, that is exactly what is it - it's called "lampblack". Do a google or yahoo search, you'll turn up many references. I have a couple modern reprints of photo catalogs from the late 1890s, early 1900's, and you see the term used quite often.

joe

**C. D. Keth** · 12-Oct-2006, 07:24

Originally Posted by Joseph O'Neil

-snip-

Yepper, that is exactly what is it - it's called "lampblack". Do a google or yahoo search, you'll turn up many references. I have a couple modern reprints of photo catalogs from the late 1890s, early 1900's, and you see the term used quite often.

joe

I always assumed they sprayed it with a fixative like you might a charcoal drawing. Guess not

**Jimi** · 12-Oct-2006, 11:04

Lamp black is originally just the remains of burnt kerosene, I've been told.

EDIT: found this on wikipedia: "Lampblack is easily produced experimentally by passing some noncombustible surface, such as a tin can lid or glass, closely through a candle flame. Lampblack produced in this way is among the darkest and least reflective substances known."

Don't blame me if your lens goes up in flames.

**Ernest Purdum** · 12-Oct-2006, 14:58

When a welder first starts up an oxy-acetylene torch, he (okay, or she) opens the acetylene valve only. This produces a very high-quality lampblack with extremely low reflectance. Chemically, I am guessing that it is very pure carbon.

**snuck** · 12-Oct-2006, 17:38

so does this mean that to touch up the coating, in order to get the blackest backs, I should be burning a big candle and holding the thing over it until it blackens? I was just going to apply matte black enamel to the interior....

**Joseph O'Neil** · 13-Oct-2006, 05:35

I'm not sure how lampblack was first applied when it was used 100 years ago, the few times I ran into the stuff myself it was so messy, i figured I didn't want to find out.

joe

**Jimi** · 13-Oct-2006, 06:31

I think candle flame to the inside of the bare barrel (without lens elements, of course!) or the welding torch method seems doable. If it doesn't work, you can always resort to other methods.

BTW, show us some photos of and with the lens when you have put it together again.

**Ernest Purdum** · 13-Oct-2006, 09:54

I guess it depends on how much you want to maintain original condition. Some modern flat black paints have quite low reflectance. Some are really not all that flat, though. It might take a little experimentation to find a really good one. Brass can also be chemically modified to a black surface. Either of these methods would be more durable than a lampblackened surface, but once the lens is reassembled, as long as no loose excess is present, durability shouldn't be a factor.

Please let us know how things work out.

**Donald Qualls** · 13-Oct-2006, 19:49

Yep, you have what was then called a "smoked" surface. A miner's lamp (a very small acetylene burner) makes a very fine smoker for this (if you can still find one, and the carbide to make it light up), though the lampblack from a candle, which includes some waxy residue, will stay stuck on the substrate better. Don't need a big candle, though; in fact, a very thin taper of the sort used for lighting other candles is best, so it doesn't drip wax. You can also get good lampblack from a wick carrying olive or corn oil, again including an oily residue that helps the carbon adhere to the surface being darkened.

FWIW, the blackest paint I'm aware of is Krylon Ultra Flat Black, but it comes only in a spray can, which makes it hard to apply inside a lens barrel (even a big one); even in my 9 inch diameter telescope tube, I'd have had to do some serious improvising had I not been able to apply the stuff with the tube laid flat, before closing the seam to form the tubular shape. In addition, there's a technique to applying it so it's really flat; if you apply too much in one coat, or recoat too soon, it'll lose most of its flatness (which comes from surface texture produced by a powder carried with the paint). Smoking is so easy to apply, and works so well, I don't think I'd bother with paint (which has a very strong tendency to gum up mechanisms, and may not adhere well to brass without serious cleaning and a zinc chromate primer).