[littlefatbuddy]

I though I would reach out and see if you would be willing to help me out. I have been mixing different chemicals to create patinas for use on mild steel. I have been able to successfully create four different patinas on a small scale basis. That is where my very limited chemical knowledge limits me. I have been working with half gallons. As you probably know, but I did not, you cannot take a perfect mix at a half gallon and mix it with another perfect half gallon and have a successful gallon. Where I need help is calculating how much chemical must be used in say one gallon, five gallons, or even 55 gallons and maintain the effectiveness of the patina.


For example, one mixture I use for a forced and accelerated rust is:

1/2 teaspoon Cupric Chloride

4 tablespoons HCL (36%) Muriatic acid

128 tablespoons  Distilled water


I had two of these half gallons mixed up and was very happy with the results. Then I decided to mix them. After that, the mixture did not work at all.


A second mixture is:

1/4 tsp SeO2

2tbsp H2SO4

85tbsp Distilled water.



So my question is can you tell me how to calculate the proper ratios and amounts to maintain effectiveness. I would be happy to answer any other questions. Even direct me to where I could learn more about it. I have seen some of the formulas where you use %w and ppv but just seeing the equation doesn't explain how to use it and the basics knowledge of why this happens.

[Borek]

To be honest, I have a hard time following what you wrote.

Have you prepared two different solutions that worked OK, but once you mixed them the new mixture didn't work? That would be hardly surprising, as the new mixture has a new composition.

Or do you ask about scaling - that is, you have a recipe that allows preparation of a half gallon of a solution that works OK, but you don't know how to prepare a gallon of the same solution? Then it is simple - just multiply everything by two.

[Arkcon]

Another thing you may be facing is the accuracy of your measurements.  I'll accept that if you try to mix a half gallon pitcher, and another half gallon pitcher, you might not reach the line of a gallon bucket.  But that's inaccuracy in measurement on your part, you ability to see the lines, or inaccuracy of the measuring vessels.

I also have to call into question your measurement scene.  To measure something, 128 times, is simply to court error.  Are you sure you didn't miscount at some point -- 127 times, 129 times?  Or can you even tell.  Google will quickly tell you: 128 tablespoons is 8 US cups, if you must use archaic Imperial measurements:  https://www.google.com/search?q=tablespoons+to+cups&ie=utf-8&oe=utf-8 

If you want to really control your formulas, you may want to purchase some laboratory glassware.  I do expect water measured in a 500 mL graduated cylinder, twice, to measure 1000 ml, as an example.  Although there can be barely significant differences with concentrated solutes in solution.  And very significant differences if we mix alcohols and water.

[littlefatbuddy]

I apologize for the confusing post. I will just focus on the accelerated rust for now. The mixture I mentioned before worked exactly as I needed it when I mixed it 1/2 gallon at a time. I had two perfect 1/2 gallon solutions and poured them into a 1 gallon container. When I poured them together it lost all effectiveness and did not react with the metal at all. The solutions were exactly the same.
I thought that by mixing the two together it would effectively multiply by two. It just did not work. I thought maybe I needed to do the calculations to get the weight by % to make the ingredients active in the larger volume of water. But I do not know how to do that. I am a metal worker not a chemist and I stank at math even 30 years ago when I somehow made it through algebra 2.
I accept that my measurements are archaic, and rudimentary. I have all the measuring vessels for Imperial readily available and that is what I used. I did not try to measure 128 tablespoons. I did however take the time to make vessels that were 5, 10, 20, and 30 tablespoons each. Could there be some inaccuracy, absolutely. But I was as accurate as possible.
Let me just take a bit to tell you how I got to half gallon. I started with solutions that I thought would be too strong. I then began diluting the solutions 10tbsp at a time until I got to an acceptable level. Three of the solutions worked out that it was acceptable to the 128 tablespoon mark. The other solution, which I mentioned in the first post, worked out to the 85 tbsp mark. It was just too weak if I added another 10 tbsp. 
Sometimes it was immediately apparent that a solution was still too strong or even too weak. Other times I would spray a few test panels and have to wait days to check the reaction. Then add 10 tablespoons and wait a few more days. I just wanted to provide that information to give a better understanding. Thank you for your time, I look forward to your other responses

[Borek]

The mixture I mentioned before worked exactly as I needed it when I mixed it 1/2 gallon at a time. I had two perfect 1/2 gallon solutions and poured them into a 1 gallon container. When I poured them together it lost all effectiveness and did not react with the metal at all. The solutions were exactly the same.

Should work this way. If it didn't work after mixing, you have made some mistake.

[littlefatbuddy]

I appreciate your response. It makes me feel not quite so dumb. I thought it should work that way too, but thought maybe there was some super secret chemistry gremlins that was sabotaging me. I decided today to start adding additional chemicals to the solution in small increments until I get back to the desired effect. I will report back when these experiments are complete. It may take some time. I really do appreciate the responses.

[littlefatbuddy]

I have been able to upscale all of the other solutions with very successful results. I upscaled them to 1 and 5 gallon solutions simply by multiplying the active ingredients per gallon to how many gallons I needed.
However, the aforementioned rust formula is still being very difficult. I can get the half gallon mix where I need it with the results I want. Pour them together and they become useless. If it matters or helps you to help me. The half gallon solutions have a slight green tint to them. As I pour them together they gradually turn almost clear and then to a light blue tint?

Finally, if I add a small amount of food coloring to any of these solutions will it change it enough to alter the desired affect?

[Intanjir]

Does the color change happen if you simply pour into an empty container?

[littlefatbuddy]

No it does not change pouring into an empty container.

[Intanjir]

Two identical solutions when added together will not react. However the physical act of mixing can cause things to happen. In particular carbon dioxide can be introduced. If that isn't your problem then something about the two half gallons must be sufficiently different from each other. It is possible that this formula is rather sensitive to the exact proportions. You may need to rethink your strategy for precision and consistency of measurements as Arkcon suggested.

Powders are not accurately measured by volume.
You really need to measure it by weight on an accurate scale.

Measuring spoons are a really imprecise tool. Too measure liquids accurately the vessel needs to be tall and thin like a graduated cylinder.

Preparing a stock solution of already partially diluted muriatic would also help.
Having it on the shelf already diluted 4 fold lets you replace measuring 4 tablespoons of concentrated acid with 16 tablespoons=1 cup of less concentrated acid. Besides the measurement advantage it is also a lot nicer to work with if diluted.

Don't use measuring cups you have made yourself unless you have already mastered the recipe and just need to make the process go faster. Custom measuring cups increase consistency but actually decrease your accuracy unless properly constructed.

As an aside, the chloride catalyzes the corrosion of copper and won't stop ever as much of it will be deposited to the surface and is never removed. The long-term stability of pieces given a patina made using a chloride based solution is not guaranteed.
https://en.wikipedia.org/wiki/Bronze_disease