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Interesting problem ... basic engineering solution

gkenyon
So, today's engineering problem goes like this.


Someone in our family is dying their hair. The chemical (probably a Chromate-based hair dye) must be mixed with 180 ml of water at between 40 and 50 °C - if the temperature is too low, mixing is very difficult, too high and the compound breaks down, and perhaps you might not get the hair colour you need.


Simples ... except we have no thermometer.


How was this quick and easy to resolve?


Parents
  • 0
    I seem to have been doing this sort of thing wrongly for months.


    To be clear I have no experience of hair dye.

    Since the beginning of the pandemic emergency, I have been washing cloth facemasks after use by mixing certain approximate volumes of cold tap water and freshly boiled water to realise the optimum soapy water temperature (between 40°C & 60°C) that should kill germs without affecting the mask's stated operational lifespan.

    All this time I had been assuming that my tap water was slightly colder than 20ºC, perhaps 17°C or 15°C and choosing the roughly measured water volumes accordingly.

    Now that I have seen GKenyon's second post above, I realise that my cold tap water must nearer to 10°C so I've just reconsidered my rough and ready mental arithmetic of how many cups (physical rather than the Imperial measure).


    Coming back to the actual hair dye problem, how critical is the temperature accuracy? Do hairdressers use thermometers for this purpose, or do they just guesstimate based on their experience?
Reply
  • 0
    I seem to have been doing this sort of thing wrongly for months.


    To be clear I have no experience of hair dye.

    Since the beginning of the pandemic emergency, I have been washing cloth facemasks after use by mixing certain approximate volumes of cold tap water and freshly boiled water to realise the optimum soapy water temperature (between 40°C & 60°C) that should kill germs without affecting the mask's stated operational lifespan.

    All this time I had been assuming that my tap water was slightly colder than 20ºC, perhaps 17°C or 15°C and choosing the roughly measured water volumes accordingly.

    Now that I have seen GKenyon's second post above, I realise that my cold tap water must nearer to 10°C so I've just reconsidered my rough and ready mental arithmetic of how many cups (physical rather than the Imperial measure).


    Coming back to the actual hair dye problem, how critical is the temperature accuracy? Do hairdressers use thermometers for this purpose, or do they just guesstimate based on their experience?
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