Can Copper Patina be Applied to Lead-Free Solder in Stained Glass Work?

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Discussion Overview

The discussion centers around the application of copper patina to lead-free solder used in stained glass work. Participants explore the chemical interactions involved, the effectiveness of different solder types, and the potential for achieving a uniform copper finish.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant notes that while copper patina solutions are available, users often report inconsistent results, such as a black or mottled finish instead of a uniform copper appearance.
  • Another participant suggests that the presence of nitric acid in the patina solution may serve as a cleaner, while copper sulfate is proposed as the active ingredient responsible for the patina effect.
  • There is a discussion about the differences between lead-based and lead-free solder, with one participant questioning whether a higher lead content solder would yield better results.
  • A participant references a displacement reaction involving tin and copper sulfate, indicating that tin may also react similarly to lead in this context.
  • Concerns are raised about the influence of other elements in the solder that could affect the deposition of copper, suggesting that minor variations could complicate the process.
  • One participant proposes experimenting with different solder sources if issues arise, indicating that variations in solder composition might lead to different outcomes.

Areas of Agreement / Disagreement

Participants express differing views on the effectiveness of applying copper patina to lead-free solder, with some suggesting it may not work reliably while others propose that the type of solder may not significantly impact the outcome. The discussion remains unresolved regarding the best approach to achieve a desired patina finish.

Contextual Notes

Participants acknowledge the complexity of the chemical reactions involved and the potential for variations in solder composition to affect results. There is uncertainty regarding the concentrations of the solutions used and how they might influence the patina application.

CWatters
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I've just starting out doing some stained glass work which involves applying copper tape to the edges of glass then soft soldering the parts together.

You can buy a Copper Patina solution that is intended to be brushed onto the solder to give it a nice shiny copper patina. However reports on various stain glass forums say this can be problematic. Some people say they get a black/grey or mottled coating instead of a nice uniform copper finish.

Most of the solutions I've found suggest the importance of cleaning the solder but I'd like to get a rough idea of the likely reaction to see if the type of solder also makes a difference.

The patina I have says it contains "Water, Selenium Compound, Nitric Acid and Copper Sulphate"

There are two main types of solder:

1) Lead Based Solder contains a mix of Tin and Lead in the ratio 60:40 (although other ratios are available).
2) Lead Free Solder contains mostly Tin (95%), silver (3-4%) and copper (<1%)

So presumably the Nitric Acid is used as a cleaner and the Copper Sulphate is the main active ingredient.

Some forum posts suggests you can't or can't reliably apply copper patina to Lead Free solder. That suggests the reaction is between the lead and sulphur leaving the copper behind? Does that sound right?

In which case would it make sense to try a solder with a higher lead content such as 40:60 instead of 60:40?

Thanks.

Edit: I found a post that suggests copper sulphate will react with tin as well as lead so perhaps the ratio doesn't matter?
 
Last edited:
Chemistry news on Phys.org
https://en.wikipedia.org/wiki/Tin(II)_sulfate
a displacement reaction between metallic tin and copper(II) sulfate:[4]
Sn (s) + CuSO4 (aq) → Cu (s) + SnSO4 (aq)
Lead, zinc should do a similar metal displacement.
Try an iron ( steel ) member to see if that form a copper surface, just for fun.

Though I don't know the concentrations of the aqueous solutions for all those reactions to be carried out.
Your patina should be somewhat dilute I would presume blue.

In preparation of the patina solution,
It could be that the nitric acid was used to dissolve copper, and sulfuric acid was added to change the 'species' so the metallic displacement would occur when applied to another metal. And they call it nitric acid, copper sulfate solution - just guessing.

see here also,
http://dwb5.unl.edu/CHEM/SmallScale/SmallScale-016.html
could explain the black color for some applications.

Not a chemist, just trying to give you some avenues for exploration.
 
Definitely displacement is what drives the deposition. Tin and lead have very similar redox potential for the X → X2+ oxidation, so they should both behave similarly.

Trick is, devil is often in details. Basic ideas are easily covered based on GenChem101 but then at some point it becomes just a black magic. Minute amounts of other elements can change the behavior of the surface and make the deposition difficult. If something goes wrong I would try solder from a completely different source.
 
Thanks folks.