Jump to content

Another type of blackening agent and some experiments

Recommended Posts

I have used ‘patina’, a blackening agent used in stain-glass work, for quite some time and for me it has worked great. I know there are other agents on the market, but I have only worked with this one. I decided to run some experiments with different concentrations and materials. Here are some of the results.


I have found that the casting material britannia is the most sensitive to blackening, so I tried to use that for these trials. I had a number of cleats shown below. First I used a scrub brush and soap to remove any release agents that are typically used in the casting process.

post-246-0-80371100-1363637129.jpg   post-246-0-41742000-1363637144.jpg


The patina is a nitric-acid base with a selenium compound. The way I understand it, the acid attacks the metal and the selenium creates a selenium oxide that is then coated onto the metal. I used a couple glass bowls, one with plain water for rinsing and the other with full strength patina to start with. Notice the light blue color. Even when it evaporates, there are blue crystals left over that can be reconstituted with a bit of water.



As soon as I put one cleat into the bath it turned black almost instantly. I pulled it out after five seconds (with a dedicated pair of tweezers) and rinsed it. The result is shown to the right in the picture above.



I then reduced the concentration by adding the same amount of water (1 : 1). The part was left in for 10 seconds and I could see the color gradually changing. This is the piece towards the bottom above.



Next I reduced the acid by adding once more the same amount of water, thus the ratio was 1 part patina and 3 parts water. After 15 seconds I took the part out and rinsed it. The result is shown above in the center. This is not enough, I thought, so I returned it to the 1 : 3 solution for another minute. It turned a bit darker, but again I don’t think it is enough. I have settled on using a 1 : 2 solution for my blackening.



Notice that even after these few tries, the solution has turned from blue to brownish. I don’t know what this is, but have found that the process continues working fine for quite some time afterwards. There comes a time when things slow down, however.


What I wanted to try and see is what would happen if I added a water-based stain or paint. Would that be incorporated in the coating? I added stain to some water, fine, and then added patina to that. It immediately reacted and the stain precipitated out. The same thing happened with acrylic paint. So forget that idea.

post-246-0-29985000-1363637202.jpg   post-246-0-70227400-1363637211.jpg


What about other materials? I have used the patina on copper, brass, solder and even steel wire and nails. So far I have found that it does not work with stainless steel. Some wires have a protective coating which can be removed quickly with some steel wool or sandpaper. I have also found that once coated the metal will not solder but bonds well with CA and epoxy. Because of that I have made wire strops and hooks with bare wire and then blackened the whole thing block and all. After a good rinse and drying, the wood did not seem to be affected. I know someone will say that acid is bad for cotton, but I still think that a good rinse will take care of that. 

post-246-0-50983000-1363637229.jpg  post-246-0-96949900-1363637239.jpg  post-246-0-89724100-1363637250.jpg

Link to comment
Share on other sites

Good job! That's one thing that is hard to get in Canada is blackening agent. I'll check out the local stained glass place for some of that solution. Thanks for posting your findings.

HSM would you do me a favor and let me know if you find some and what you think after using it. Other than JB it seems that we are the only two who have used this stuff and I am surprised that others have not come across this. Maybe the two of us have just been lucky.

Edited by Modeler12
Link to comment
Share on other sites

I just read some of the horror stories on the other thread about blackening metals and I am amazed. As I showed above, I have not had any significant problems with any material such as solder, brass, copper, ordinary steel (exclude ss) and britannia. Indeed make sure that there is no coating on any of these (particularly wire) and then go ahead. I have touched the metal before blackening: no problem. I have used it after soldering brass and steel wire: no problem. I have . . . well you get the idea.


One thing I did not mention is that the patina leaves a black coating on the surface. If you leave the part in much longer than 'just right' the coating becomes heavier and afterwards will rub off as a black 'soot'. That is the selenium oxide and you should wash your hands afterwards (don't smoke). If you have to leave the part in the solution for more than a minute you are simply using it too diluted. See my experiments above.

Link to comment
Share on other sites

Thanks Jay,


Very informative experiment and tips.

You know Mark, I still find that I do not follow my own advise all the time.


Just this afternoon I pulled out some pre-assembled blocks and lines for my rigging. The blocks had brass wire for strops and I noticed the wire had not been blackened yet. I dipped them in my 'solution of choice' and   . .. by golly, they did not blacken! The solder joints looked fine, but not the rest. Sure enough I had forgotten to clean off the polymer coating on the brass wire. . . . . 

Link to comment
Share on other sites

Here is one more experiment. The question was raised about cleaning brass wire before blackening. I know that some wire you buy in craft shops has a polymer coating to prevent tarnishing. But what about some of the others?


Here is what I did. I took samples off three kinds of wire.

1.Steel wire used by florists. This happened to come from China.

2. Brass wire from a craft shop.

3. Copper wire I had lying around and I have no idea if it was coated or not.


One of each I used 'as is', the other piece I 'cleaned' with some steel wool. Then I dipped each one in the reduced solution of the patina as discussed above (2 parts water : 1 part patina). I held the piece with my fingers at the end (bottom part) and submerged it for about 10 to 12 seconds.




1. The steel wires turned black almost immediately.

2. The brass 'as is' had a couple small black spots but really was not affected. The piece I had 'cleaned' had more black showing, but not really enough!!! Hmmmm. . . 

3. The copper 'as is' turned black but again not a deep black. The cleaned copper turned uniformly black.



I knew that the brass should have done better. So I repeated the experiment using straight patina out of the bottle. And sure enough the sample I had cleaned with steel wool turned black almost instantly. It only goes to show that the concentration of the solution has a lot to do with the material you are trying to blacken. 


My suggestion is: TRY IT YOURSELF.

Link to comment
Share on other sites

So maybe a stronger mix for brass.


How durable is the blackening once rinsed and dried, will it rib off easily down to metal or does loose black come off but black plating remains?

Edited by BareHook
Link to comment
Share on other sites

So maybe a stronger mix for brass.


How durable is the blackening once rinsed and dried, will it rib off easily down to metal or does loose black come off but black plating remains?

Good question. The coating does not completely rub off. What happens is that if the coating is very thick, some of the 'soot' does come off but the base remains fine. In fact, if you rub it with a paper towel the surface shows a nice sheen. 

I took the sample I used above and gave them a quick rub with a paper towel and you can see the results.



Will it last? I have used this stuff on stained glass windows about 20 or 30 years ago. One piece has been outdoors (on my tool shed door) and the black is still there. Also have a look at the gun barrels I treated about a year ago http://www.brentjes.com/Conny%20Deck.html#black


There are three pictures of a gun barrel with one treatment, two treatments and after rubbing it with a paper towel. I don't remember the concentration I used at the time.

Link to comment
Share on other sites

Please, what was the material used to cast the cleats?

Britannia. It is an alloy made up of zinc, lead and a little antimony. It is the same as pewter, but both can vary in composition, melting points and other characteristics. Britannia melts at a low temperature and is easy to cast, hence it is used for our small parts such as the 'cleats'.

Like I said, I have used the patina on lots of pieces made out of this material including the larger gun barrels and anchors.


Before someone comments, let me correct myself. The pieces I used for the experiment were 'chocks', not cleats. They are all part of the metal pieces supplied in the USS Constitution kit.

Edited by Modeler12
Link to comment
Share on other sites



This has been a most informative thread. I think all of us have had problems with the usual variety of modeler's blackening agents - all with similar results. The blackening either isn't permanent and comes off on your fingers or doesn't affect the metal at all.


I will have to dig out my toolbox with stained glass supplies and see if there is any of that patina there. I don't recall having used it in the past.


The most common problem that I've seen with this process is getting a permanent oxidation of the metal, so this interests me quite a bit.


Thanks for the experiments and so forth - that's the kind of "time well spent" research that helps all of us.

Link to comment
Share on other sites

Thank you Hank for those comments.

Please allow me to post a couple results that I think are worth repeating:

1. The patina I used, Novalac, has been very effective on most metals and has had good reviews by people who have used it for several different applications. 

2. The metal should be cleaned, brass wire should be sanded or rubbed with steel wool to remove any coating.
3. The concentration of the solution should be checked for the particular metal you are working with. Brass is slower or requires more acid than copper or solder, for example.

4. Don't over-treat. The extra selenium oxide will rub off and you should be careful with the 'soot'. 

5. Rubbing the final coating with a paper towel will not wipe off the coating in total but will impart a nice sheen.

6. Don't try to solder any metal that has been treated unless you sand off the coating first. Bonding with CA or epoxy works fine.

7. The coating will remain in tact for many years.

Link to comment
Share on other sites

  • 2 weeks later...

The question about blackening brass wire keeps coming up. Again if using some steel wool or sandpaper cleaning does not do the job for you, here is another option.


If you are going to use the wire for strops or other parts that require soldering, do that first. I like to coat the wire with a thin layer of solder and then make the solder joint. I show this below for some tiny cleats I needed.

post-246-0-87723900-1364871641.jpg  post-246-0-37889900-1364871586.jpg

After I trimmed the ends, I blackened them in the 1 : 2 solutions. As you can see that worked fine on the solder ends and only so-so where the brass wire was still exposed (the very end was not in the solution).

post-246-0-33009100-1364871630.jpg  post-246-0-84495900-1364871612.jpg

These were very tiny cleats (I rejected one) that are for some thin halliards coming from above.

Link to comment
Share on other sites

  • 10 months later...
  • 1 month later...

Really interesting posts, I haven´t decided yet to paint the cannons of my Vasa with undercoat black paint spray (as Nazgul reccomends in his post) or with Patina product.  I just obtained a little of patina liquid and will make some tries first.



Link to comment
Share on other sites

Hi all,


I use this same product, which I got from MicroMart. I've found that the best way to clean the parts was to soak them in acetone. After drying, and using tweezers, I put them in a glass container ( shot glass). Brass, copper and steel blacken almost immediately. After several seconds, using tweezers, I let them dry on a paper towel.


I've never had a problem others have experiences, but I've never tried Britannia.


Regards, Rick

Link to comment
Share on other sites

  • 1 year later...

Acetone is good for cleaning crud but in a confined space will kill you. We lost an electrician when he was behind a fan motor in a corner. Legs were sticking out but wasn’t found till to late. Believe the fumes like gasoline fumes collect on the floor. USS Helena CA 75 1962.


Edited by shiloh
Link to comment
Share on other sites

  • 5 weeks later...

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.

Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.


  • Recently Browsing   0 members

    • No registered users viewing this page.
  • Create New...