How did they blacken the metal stops & caps of the Daguerre era lenses?

[Ron (Netherlands)]

Have found a nice old lens of the Daguerre era which is missing its stop disk (is that the right word?). I guess these disks/plates were made from brass but I'm not sure since I have no original to compare.

Questions:

1. From which metal was the stop disk made?

2. How was the metal blackened?

3. Is there a source for the screw used to attach the plate to the lens? (the screw has a little tapered base - guess it could also be replicated by a machinist)

Here is a picture of an early achromat with a metal stop disk - at one end it is fastened to the lens with a screw, so it can open/close the lens:
(If anyone has one laying in a parts bin I would be most interested of course....)

https://live.staticflickr.com/65535/51394050809_1b6c13e42f_c.jpg (https://flic.kr/p/2mivWLi)

[RichardRitter]

Liver of sulfur,

[John Layton]

Richard...ya gotta give us more details - otherwise "liver of sulfur" just sounds...really unappatizing!

[cowanw]

https://www.amazon.ca/BeadSmith-XTL-8010-Extended-Sulfur-Oxidation/dp/B004PLZ4SS/ref=asc_df_B004PLZ4SS/?tag=googleshopc0c-20&linkCode=df0&hvadid=335224427030&hvpos=&hvnetw=g&hvrand=2151365642243654123&hvpone=&hvptwo=&hvqmt=&hvdev=c&hvdvcmdl=&hvlocint=&hvlocphy=9000873&hvtargid=pla-309695612066&psc=1
from Wiki - Liver of sulfur is a poorly defined mixture of potassium sulfide, potassium polysulfide, potassium thiosulfate, and likely potassium bisulfide

[CCHarrison]

lamp black

[Havoc]

Lots of options here. One from a 1936 lab manual: https://aip.scitation.org/doi/pdf/10.1063/1.1752115 Selenium dioxide is another one and you can find that around in ready-made products (poisonous!).

[Richard Wasserman]

You can try this— https://www.birchwoodcasey.com/products/brass-black-touch-up-3-fl-oz-bottle.html

I used to use this in antique restorations. It may not be quite as black as the original you showed, but the blackness can be enhanced a bit with a clear top coat.

[goamules]

They painted or treated the inside of brass barrels in a variety of ways. Waterhouse stops were done chemically to retain the black, when they scrape in out and out of the slot. Selenium Dioxide is reputed to work well today, read the MSDS.

See https://books.google.com/books?id=EV9QAQAAMAAJ&lpg=PA502&ots=wODs2isvqw&dq=chemically%20blacken%20brass%20lens&pg=PA535#v=onepage&q=blacken&f=false

[Steven Tribe]

There are two previous threads on the permanent blackening of brass!
Here is my contribution on a previous occasion!

Yes it is ordinary sheet brass.
Ordinary small Metric screws.
Thread cut in top plate - if necessary. Oversized thread, perhaps - only 3/4 through.

Remember there is a smart variant with different sized apertures - as well as the basic “shutter”.