Weird brass surface

[Chriske]

Hi guys,

Sorry to post this in HMEM forum. But I have no other option left. I've asked in telescope related forums to no avail. I hope some willing soul on this forum can help me explaining what went wrong with this tube.
As you can see this tube has a few issues.
It suppose to be made in de late(maybe mid) 1800's and looks very weird. It has lots of cracks, LOTS, and the surface is very rough. I think the roughness is caused by very course sandpaper or even a file. Later on someone treated the tube with varnish.

I'd like to restore this telescope, bring it back to life and give it back it's original shiny surface. Maybe because of it's roughness it is no option anymore. Just need to know before I start working on it.
This instrument is a Bardou telescope btw.

To be clear I am familiar with brass and bronze. You can see a few Stirling engines almost completely made of brass. But regarding this particular problem I'm a bit confused...
Can someone help me please...

Chris

Same crack near/closeby

Surface roughness

 

[aka9950202]

The cracks are from dezincification. Basically the zinc has started to leach out of the copper alloy. It may need professional restoration but "museum type" restorers. I had a brass box from the late 1800 crumble in my had while washing it off with water.

The polishing should only be attempted once the cracking issue has been resolved.

cheers,

Andrew inMelbourne

Hi guys,

Sorry to post this in HMEM forum. But I have no other option left. I've asked in telescope related forums to no avail. I hope some willing soul on this forum can help me explaining what went wrong with this tube.
As you can see this tube has a few issues.
It suppose to be made in de late(maybe mid) 1800's and looks very weird. It has lots of cracks, LOTS, and the surface is very rough. I think the roughness is caused by very course sandpaper or even a file. Later on someone treated the tube with varnish.

I'd like to restore this telescope, bring it back to life and give it back it's original shiny surface. Maybe because of it's roughness it is no option anymore. Just need to know before I start working on it.
This instrument is a Bardou telescope btw.

To be clear I am familiar with brass and bronze. You can see a few Stirling engines almost completely made of brass. But regarding this particular problem I'm a bit confused...
Can someone help me please...

Chris

Same crack near/closeby
View attachment 152048View attachment 152049

Surface roughness

View attachment 152050

Fr

 

[Mike1]

I think the term is Season Cracking see this Linkhttps://onlinelibrary.wiley.com/doi/abs/10.1111/j.1559-3584.1913.tb01979.x

 

[GreenTwin]

Brass should not be used on boilers in contact with steam since the zinc will leach out, and the part will fail.

The white paper seems to indicate that forming the brass is what causes the problem.

I have not seen that on cast brass parts.

I have never seen it on rolled copper sheet, so I suspect the zinc that is added to the brass may be part of the problem.

The white paper also mentions that some bronzes may have this problem, but some bronzes have a bit of zinc in them.

Zinc parts of old were renowned for crubling over time, and thus the term "pot metal".

Modern zinc alloys are suppose to be more stable.

My guess is that the forming/rolling action is breaking down some of the molecular bonds, possibily in metals that many not fully alloy, or different alloys that have a weak bond.

In aluminum, if you pour too fast, you can churn bifilms into the molten metal, which is caused by rolling the solidified outer skin of the aluminum back into the flowing molten mix. This causes a lot of problems that don't immediately show up in a casting.
It is critical to control velocity, and use a laminar flow when filling a mold, to avoid having problems in the casting.

I can't help on how to go about repairing that.
I would almost think some sort of electroplating over all of it may provide a temporary fix.
I am not sure about a permanent fix.
A good museum would know what to do.

A 2" very fine ceramic sponge in a tool and die grinder or something similar will give a mirror finish on metal.
You have to use it very lightly, so as not to gouge the surface.
.

Edit:
One mistake that is made almost univerally on ytube (with the exception of olfoundryman) is that people enthusiastically stir their aluminum like crazy, adding usless "degassing" agents that are not degassing agents, and encouraging and emphasizing that everyone else should do the same.
Its a real blunder to stir all the bifolds into an aluminum mix.
Washing soda does nothing as far as degassing aluminum; the gas you see is moisture absorbed into the soda.
If you dry your washing soda in the oven, you will notice that it produces no gas at all when added to molten aluminum.

Every bifold is a cold joint between two of the solidified layers of aluminum film, and the ruin the structural integrity of a cast aluminum part.
You can see these bifolks in a section of the casting, and they are distinctly round.
1st Rule of Aluminum casting: NEVER stir the melt !
2nd Rule of Aluminum casting: Melt as quick as possible, and pour immediately when you reach pour temperature.
Don't overshoot the pour temperature. Don't use washing soda; it serves no purpose in casting work.
.

 

[Chriske]

Thanks guys for the replies.
I received another reply elsewhere, he also mentioned the dezincification problem.
He also said replace the tube, the most logic solution.

 

[Steamchick]

Mike1:
Thanks to the article on "Season cracking". Most interesting. Somewhere in my dim and distant past I recall my Grandfather (an ex-Marine Chief Engineer) telling me about repairing clock parts and a brass plate that had cracked... Possibly after I had shown him my school metalwork practice piece of planishing? - From all I recall he said a lot of hand made brass-work and copper-work from the Middle-East was made by planishing. A technique going back to the Bronze age, and un-changed in the Middle Eastern countries, and all across Asia. (He was on ships there during WW1 - Gallipoli, Alexandria, etc.). I remember seeing a brass plate with lots of cracks, and he explained that planishing, if done on poorly annealed brass or copper could set up "forces" in the metal that later caused the metal to crack - "forces" explained to an 11-year old would be residual stresses.... Copper plates, and bowls much less likely to crack apparently (?). The brass plate I remember was from a neighbour, who had the "antique" plate in a cupboard and found it cracked "when getting it one day to show someone". I don't know how he repaired it - possibly silver soldered? He repaired clocks and watches by making new parts for worn, or broken parts, but the plate needed repair...he showed me how the cracks had followed the sharper folds in the worked pattern on the brass...
Thanks for the memory!
K2

 

[Mike1]

Hi Steamchick,
Nice to hear the article brought back memories for you, it also explained for me why the case of a very old brass barometer we have, also has small cracks.
Mike1