# making patinas for copper

Copper nitrate, calcium carbonate and ammonium chloride mixed will patina copper green. I need to know

• If calcium carbonate should be a heavy powder or a reagent.
• If calcium chloride is a dehydrate or reagent.
• If ammonium chloride should be granular or granular reagent.

These mix with water in equal parts. Im not a chemist, and this is for a sculpture with a recipe from an old metal techniques book.

• Hmm... "These mix with water in equal parts." So if 4 kg of solution were being made then 1 kg of calcium carbonate. I can't image that much calcium carbonate would dissolve in 1 kg H2O, 1 kg CaCl2 and 1kg NH4Cl. – MaxW Feb 15 '17 at 21:56
• When making the solution you might want to heat it to help everything dissolve. Suspect you don't have a lab, but with any reasonable precaution these particular chemicals would be fine to heat on kitchen stove. There are very few chemicals that I would use in my kitchen. – MaxW Feb 15 '17 at 22:01
• Could it have been calcium bicarbonate instead of calcium carbonate? – MaxW Feb 15 '17 at 22:33
• @MaxW, calcium bicarbonate is not a stable solid compound as it readily looses $\ce{CO2}$ and water to form calcium carbonate. – airhuff Feb 15 '17 at 23:06
• Yea, I'm sure it's being made in solution like you say. – airhuff Feb 16 '17 at 0:23

Nothing about your process is quantitative in nature, nor does it require high-purity reagents. So most definitely do not invest in reagent-grade anything. To answer your questions in order:

1) The "heavy powder" calcium carbonate will be sufficient. It may be "clumpy", in which case you will want to physically break it up prior to mixing it in with the water. You should wear rubber gloves and a dust mask if you need to do this. The only purpose of this compound in your procedure is to raise the pH.

2) You definitely do not need anhydrous or dried calcium chloride. You are not trying to quantitatively measure out this compound and you are just going to put it in water anyway, so hydration is not an issue for you at all. The purpose of this reagent (generic term, not referring to any "grade" or purity) is to provide chloride ions, that at high pH will form a layer of cupric chloride, which is green when it absorbs water from the air to form cupric chloride dihydrate. Again, this will be a product of your procedure and the degree of hydration of the calcium chloride is not relevant. As in step one, this compound may be clumpy and if so you should break it up as described there.

3) The phrase "should be granular or granular reagent?" is the key. As stated above, there is no need for reagent grade materials for your process, so if your options are "granular" vs. "granular reagent" then just get the granular, not the granular reagent ;) The role of this compound is to both raise the pH and to provide chloride for the purpose described in step 2.

Again, it may be tempting to think you will get a better patina by investing in expensive reagents, but for your process that would simply be a waste of your money to buy reagent-grade anything if there is a lower grade alternative.

• airhuff, thank you for this information. Its exactly what I was hoping for. Obviously I`m no chemist, but with your answers, I can move forward. All of these chemicals are available at Amazon. So because of your generous help, I can purchase and mix like a pro. [???] Again, thank you very much. Ken – ken Feb 16 '17 at 23:00
• Awesome! So glad to help. Note that the way we say thank you here is to accept (and upvote if you like) the answer ;) Cheers... – airhuff Feb 16 '17 at 23:03
• airhuff, will be glad to vote and show acceptance. How I do Dat. – ken Feb 16 '17 at 23:08
• There is a checkmark to the left of the question, below that big number 2 between the arrows. If you think the answer was particularly good, it's your choice if you then want to hit the arrow above the 2, changing it to 3 (meaning 2 other people have upvoted it). And dat's how dat works! Appreciate it. – airhuff Feb 16 '17 at 23:11
• I meant the checkmark is next to my answer, duh, sorry. – airhuff Feb 16 '17 at 23:15