HA experiments: What did we learn?

We had a live webchat at 9pm on Monday 3rd April looking back at the Hydroxyl Apatite project.

Main findings

Sophia What do we think we’ve learned from the experiments then? TBH, I feel like I know less about HA and nappies now than I thought I did before!
Iona We found HA again on some test nappies which was good. But we also found calcium carbonate which has confused the issue
Sarah and the zinc thing too
Iona Yes, the zinc was another new and interesting finding. I was so disappointed for the dip and dry testers that nothing was found on those samples!
Sophia I know! And I felt bad for the people who’d dealt with the wee smelling boosters for a month, to no avail.

Experiments don’t always work like we expect

Sophia Iona- you did a science PhD, was there a lot of doing experiments and finding nothing?
Iona Absolutely.  At times it felt like my entire PhD was about finding nothing! And the experimental results you do get, just lead to more possibilities. So I’d say this is fairly typical! But they inspire and challenge you to do the next set of experiments.
Sophia Even though I have a science degree, most of my education involved doing ‘practicals’ rather than real experiments. So maybe it trains you to think that you will get results every time.
Iona Ah yes, the difference comes when you design your own experiment, rather than follow a tried and tested method!
Iona My undergraduate project also didn’t work!
Sophia Also, science documentaries and news stories are all about the times they DID find something. False advertising!
Iona The news don’t want to hear about what you didn’t find! And its actually a big issue in science. People don’t publish null results, so the next group waste money repeating experiments that don’t work. But who wants to say ‘I spent the last 5 years doing X and it didn’t work’
Sophia Ha!

Why didn’t the experiments work?

Sophia If we could do more experiments, what would they be?
Sarah I suppose the no results lead you to creating a trial or experiment that does have a positive answer so you can get the glory of finding out something new?
Iona And we did find things  HA, Calcium Carbonate, Zinc, a trend towards an increase in pH during dry bucket. Sarah- did you do the pH tests or dip and dry experiments? I’d be interested to see what would happen with dip and dry, if we used a combination of urine and detergent together  but I’m less sure I’m volunteering to smell it
Sophia And maybe urine can form HA, but it needs to be urine with a high calcium content or high phosphate content (or both!) and we just didn’t happen to have that with the children who’s wee was used.
Sophia So maybe we would need to test a lot of wee to find the right conditions.
Nicola Having a little read through the chat so far, I was pretty disappointed we didn’t get the results we wanted!  I thought perhaps we would get HA from the dip/dry experiments
Iona I really wanted the dip dry to work
Iona I wonder if toddler wee contains less calcium because they are partly weaned?
Iona The calcium carbonate that Shirley Technologies found is an interesting side angle
Sophia We could dip boosters in adult wee?
Nicola I wondered about the toddler wee not being right for the nappies while doing the experiment but then forgot to ask about it!  I figured it would be quite difficult to get babies wee unless people were doing EC
Nicola Not keen on that one Sophia!
Iona Much easier to get samples of adult wee! What effect would last nights glass of red wine have? Or do we need to drink Bailey’s to increase calcium?
Nicola I think more wee testing would be helpful, but perhaps with younger babies, breastfed and formula fed to check if one would be more likely to have HA or Calcium Carbonate
Sophia I volunteer for that one! (The drinking baileys)
Nicola Haha!

Wanted: baby wee expert

Iona We never managed to get a baby wee expert to talk to us unfortunately. I emailed about 10 of them! They probably thought i was mad!
Nicola I didn’t know there was such a thing as a baby wee expert!
Iona I emailed infant urology consultants. Doctors who deal with kidney issues etc. But they are probably too busy
Nicola Good idea Iona, that would have been helpful had they been able to join in.

Why is there more hydroxyl apatite in certain nappies?

Sophia I still find it really strange that so many of our first lot of test nappies had loads of HA, but then the more recent lot  some of them had HA, but none had as much.
Iona Were they as ‘problem’ as the first lot?
Sophia Maybe not as problem as the first lot
Nicola Am I right in thinking the first lot of nappies with the HA were pre-loved so unknown history?
Sophia I think some of the first lot were preloved, but some weren’t.
Iona It was interesting that the highest HA/CC was found on a wipe, not a nappy
Iona 15.6%, which is getting close to the results from last time
Sophia Summary of the results and washing history of last year’s test nappies https://nappysciencegang.wordpress.com/2016/11/06/apatite-for-destruction-the-hypotheses-so-far/
Nicola Do we know if the wipe was stored wet before use?  That might indicate it’s the water causing the HA as opposed to the wee or detergent
Iona That is an interesting question
Sophia Good question

Wipes and wet pails

Iona I was thinking that the wipe will have been drenched in water and then stored, but of course it may have been stored wet before use too.  And ASR did claim to have very hard water
Nicola I keep my wipes damp in a tub ready to use, I thought a lot of people did the same rather than wet as needed so it would make sense. And Jennifer told us her student created HA from very hard water didn’t she?
Sophia Yes, although they had also added phosphate
Nicola Ah ok
Iona Do we know where ASR lives and if phosphate may be added to her water?
Nicola Lack of scientific knowledge here, am I right in thinking phosphate is like salt?
Iona Nicola- I think you are right, most people store wipes wet. I forget, as we store them dry and wet as we need them.
Nicola Or what would cause phosphate to occur naturally perhaps? I guess everyone does things a little differently Iona, would depend on your facilities at home and what’s easiest!
Sophia (BTW, ASR is actually AJR, Ian misread her writing)
Iona Oh yes, I forgot
Sophia I think the wipe had 15% ash, but it was more calcium carbonate than HA. So it could be that how she stored the wipes or something made CC more likely to form.
Nicola Perhaps she used something other than just water too?  We will need to ask her and include it in the write up
Sophia Good thinking
Iona Sophia- did you get her postcode? Maybe we could look up her water supplier? And there was the calcium hydroxide that CCI found formed at low calcium concentrations. I wonder what determines whether calcium hydroxide, calcium carbonate, or HA forms?
Nicola Good question Iona
Sophia I’ll check
Iona I’m guessing you will check postcode Sophia, rather than having a magic answer to the chemistry question! Maybe if she took part in pH experiment? Nicola or Sarah- did you do the pH or dip dry experiment?
Nicola I did PH and dip dry. I am in very soft water area though
Sophia The form for submitting the nappies was the one Grace did and I don’t have access to the answers
AJ I’m here, sorry I’m late 3 year old up
Sophia Hi AJ! We are just discussing your wipe
AJ Will just try and read back. Saw fb quickly. My wipes are stored dry before use and wet (for a good few days) after use
Nicola That’s interesting, I thought storing wet first would have caused the HA but obviously not!
Iona AJ- do you use any oils on the wipes?
AJ I wet as I breed it on the day of using. I’m in a ridiculously hard water area. It’s a private, borehole supply
Kate Hi. Sorry so late. Rubbish internet here.
Nicola I don’t know why I think that… after wiping there can’t be much wee on the wipe to be reacting with the water?
Nicola Did anyone who wet-pailed offer to donate nappies?  That might be an interesting experiment
AJ Mixed re oil. Not on dry wipes but I do on wet ones. It’s cheeky wipe dirty oil
Kate Did we have any info about how the calcium carbonate presented itself. Was it an exoskeleton like the HA, particles trapped in the fibres?
AJ Is cc directly linked to hard water? I’m really surprised my nappies weren’t loaded as they were so crusty
Sophia Kate- Further analysis showed that in all cases the residual material was intimately associated with the fibres of the tested fabric, and formed a skeletal residue when the washing removed the cellulosic fibre.
Kate I remember that if you use soda crystals calcium carbonate is what you get when it reacts with calcium water hardness ions, which is why I wondered.
Iona AJ- do you have any idea if phosphate is added to the water in your area?
Kate Wow so it was a similar form. Does that mean it has formed by crystallising in drying, same as HA, I wonder.

Crustiness and hard water

Nicola AJ- can you describe crusty?  Like the way bamboo gets a bit hard then softens up if you rub it or tumble dry, or like crusty that won’t go away no matter what you do?
Sophia AJ- I guess your nappies were the only ones that had ONLY HA in them. Although it wasn’t as high a proportion as the ones we got tested last year.
AJ I was disappointed as it leaves more questions than answers
Sophia I wonder why AJ’s nappies had only HA, but the wipe had both CC and HA, but more CC.
Iona AJ- I think you said you wash wipes and nappies separately?
Nicola Oh, I think I read something about limescale and calcium carbonate when I was looking to see what CC was, perhaps it was the machine that caused it
Sophia It’s strange, isn’t it? If they feel dry and rough, what is causing that, when the HA content is not THAT high?
Iona Towards the end of last chat I asked if AJ knew if phosphate was added to her water supply?
AJ Yes I wash separately as otherwise they get too tangled up. Could overdosing of powder be an issue? I always had an overfoaming machine when washing wipes as microfiber reacts strangely in the wash
Iona AJ- if you wash separately, our theory about urine being important could be flawed
Sophia Calcium carbonate is what limescale is made of, so if your washing machine was full of limescale, then it looks like there’s lots of CC in your water.
Iona AJ- does anything else get rough e.g. towels
AJ Yes everything gets rough. I add softener to everything but nappies and wipes

Can crustiness be reversed?

Iona If it is limescale, then would vinegar remove it?
Sophia Or citric acid.
AJ I’ve been reading lots about vinegar! I’ve just bought a stash for cleaning with
Nicola Experiments to see what removes it?!
Iona Citric acid was suggested by Prof Darvell as a potential for removing HA
AJ It did well on my drainer better than I thought
Sophia Presumably citric acid would work on CC too?
AJ Can you add it into the wash?
Iona I assume so, it is a stronger acid than vinegar
Nicola From nappy lady website:  Vinegar has traditionally been used as a nappy soak however many nappy manufacturers including Totsbots, Bumgenius and Bambinex now specify that vinegar, or any soaking agent including Bicarbonate of Soda, Nappisan, bleach or harsh stain removers should never be used as they can corrode the nappy fabric and effectively destroy your nappies. Please note that if any of these products are used on the nappies or accessories it will invalidate any product guarantee. Bamboo is an especially delicate fabric and is particularly susceptible to harsh chemicals.
Iona Sorry assume so was to the citric acid removing cc
Sophia Prof Darvell thought citric acid would work better than vinegar because it makes the mineral you remove stick together in clumps (I think he said it’s a chelating agent and I think that’s what that means)
Iona Yes, he suggested an overnight soak in citric acid and then several hot rinses. For the chelating part, soaking is important ‘no quick rinse’ he said. I think any extreme measures will invalidate warranty
Nicola A lot of things seem to invalidate the warranty, I suppose if they are already quite bad that may not be a concern though?  Just thought it might be relevant
Iona Very relevant
Nicola AJ- I’m curious, have you tried to strip by leaving out in the rain to see what that does?
AJ I leave them out regularly in the summer, not so much in the winter. It’s all our clothes, not just nappies. My little boys jeans stand up in their own!
Iona oh dear
AJ More experiments are needed for sure but on what specifically
Nicola We were saying in the last chat more experiments on wee might be needed. Although with all this talk of your washing I’m thinking more experiments on hard water would be good!
AJ Interestingly are about to move house and are thinking about getting a water softener  would be interesting to compare
Iona You can read Prof Darvell suggestions for experiment at: https://nappysciencegang.wordpress.com/2017/01/15/ha-solubility-email-chat-with-prof-brian-darvell/ It would certainly be interesting to see if a new nappy went crusty with a water softner installed
Iona Or if your existing nappies ‘softened’ over time
AJ I’m hoping anecdotal evidence will say that
Nicola Ok I need to go now. Night all!
AJ Shall we call it a day?
Iona I think we probably should. Goodnight and thank you.


  • We found hydroxyl apatite and another mineral deposit on nappies we tested.
  • We did not manage to create hydroxyl apatite in our experiments.
  • There are aspects of infant urine and nappy washing/drying practices that we don’t fully understand that probably affect mineral deposits on nappies.

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