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Don’t believe everything you read!

Posted: Tue May 16, 2017 10:22 am
by richardh08
During my experimentation with crackle compositions, I have seen many reported formulations that, on testing, I have found not to work. Patent applications, especially those emanating from China, seem to be written with sufficiently vague specifications that the effects they claim are almost impossible to reproduce. I’ve learned not to believe any reported composition unless I know it to come from a reliable source.

Last week I spent a very pleasant morning chatting with a respected member of the professional community. Amongst other things, he told me a couple of stories about his experiences with Chinese manufacturers. In a list of the contents of imported fireworks, he noticed that copper oxide was listed more than once, each listing being accompanied by a different Chinese ideogram. He concluded that there must be something different about each of the copper oxides that appeared in the list.

On another occasion, during a visit to China, he saw an (unspecified) effect that he wanted to try, and was given the formulation, which contained copper oxide. On returning to the UK, he found he could not reproduce the effect that he had seen and got back in touch with his Chinese source. He was told he needed to use their particular type of copper oxide and they sent him a sample. He didn’t say whether it worked or not, but he did tell me that he found the ‘copper oxide’ to contain 17% potassium dichromate! He gave me a small sample and I've just run a quick and dirty solubility test on it, which confirmed the dichromate content to be about 15%.

The implication of all this seems to be that reported compositions are not only likely to be approximate in terms of the stated proportions, but may also contain unlisted ingredients. In the above example the unmentioned component is both toxic and carcinogenic, so I have to ask myself: how many other such cases exist?

Re: Don’t believe everything you read!

Posted: Tue May 16, 2017 2:46 pm
by Pyro-Gear
Well like a said to you the other day CE marking stands for Chinese export no surprise that dichromate has been found in the copper oxide.

The most interesting thing is why, as dichromate is not cheap even to the Chinese.

Genuine CE marks are crippling the UK and Europe in the manufacturing of fireworks bring back the old British standards I say but I think it’s too late for the gentleman in question.

Re: Don’t believe everything you read!

Posted: Tue May 16, 2017 4:58 pm
by sambo
Yes - you're right Ken. I think it was Dr Wan's special copper Oxide mix.

Re: Don’t believe everything you read!

Posted: Tue May 16, 2017 5:29 pm
by Pyro-Gear
Or maybe the Indian magic mix Sam

Re: Don’t believe everything you read!

Posted: Fri May 19, 2017 7:02 pm
by biffo
I don't understand why the country in question is exempt to all the normal import checks,watch fake Britain any week and we seem to import any rubbish and sub standard goods that can be imagined.Regards B

Re: Don’t believe everything you read!

Posted: Wed Jan 02, 2019 9:12 pm
by dave321
would the inclusion of the dichromate reduces the activation energy for the copper oxide reactions ?

Re: Don’t believe everything you read!

Posted: Sun Oct 18, 2020 10:55 pm
by Colour_the_sky
In one chinese patent I found for copper oxide MgAl crackling that they wanted to bind the inner and outer part of the crackling with water based dextrin to avoid using more expensive plastic binders and they found out that the inclusion of potassium dichromate makes a barrier between inner and outer mix to avoid kno3 and other unwanted chemicals leaking inside the crackling and taking of the sound.

Re: Don’t believe everything you read!

Posted: Mon Oct 19, 2020 6:22 pm
by dave321
i would have thought that it was more of an attempt to protect the magnalium,
if it was needed, which may be doubtful

Re: Don’t believe everything you read!

Posted: Mon Oct 19, 2020 6:37 pm
by Lloyd
I agree, Dave.

In fact, in some formulae, Mg/Al does need protection, and potassium dichromate works well for that.

But I doubt it would be necessary in a crackle formula, unless the copper oxide was contaminated. (likely, with Chinese materials!)

Lloyd

Re: Don’t believe everything you read!

Posted: Mon May 24, 2021 8:29 pm
by Colour_the_sky
If the outer mix contains KNO3 and you use water do you have use dichromate then ? All I remember was If you mix in 20% KNO3 the crackle doesn´t work anymore.

Re: Don’t believe everything you read!

Posted: Mon May 24, 2021 9:33 pm
by Lloyd
If there's _any_ KNO3 in the basic formula, you need to pre-coat the Mg with dichromate. If there's only KNO3 in the prime layer, it's still not a bad idea to use dichromate-water instead of plain water as the wetting agent.

And even then, don't expect it to have a long shelf-life.

Lloyd

Re: Don’t believe everything you read!

Posted: Thu May 27, 2021 8:41 pm
by Colour_the_sky
I do it like the chinese hate it but it works better for me and I also leave the dichromate out. I explain why the chinese hate it because I use water for the crackling mixture which would be ok for them but the outer layer or prime you call it I use pvb and alcohol instead water and dextrin what chinese would prefer the reason why they hate it is pvb is more expensive than dextrin and of cause your world goes down If you don´t safe some pennies. As I said above the reason why I went to solvent based prime is it can´t drive in any KNO3 in the crackling even without dichromate but with water and dichromate I didn´t try that because I don´t have any dichromate.


Would you use dichromate even when the prime is non water based ? I have the feeling sulfur and mg also don´t like each other even with solvent based binder I smell sulfur dioxide gas. Next time I try to leave out sulfur when I use metals. I also don´t want a slow corrosion when in storage. Oh one thing I could try is to coat the crackling with a protection coat of linseed oil If that also helps with storage. I can´t get any dichromate here thats why I would prefer that. I just wanted to know If you need linseed oil when you used pvb as your binder in your prime or If that gives some protection too? I could also use pvb to cover the crackling instead linseed oil I have both but pvb is faster in drying :)