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Strange stain in caravan

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Peter G. Shaw20/08/2021 11:53:05
1314 forum posts
44 photos

Hi folks,

I'm looking for ideas on what may have caused some strange dark(ish) grey stains in the mugs and the kitchen sink of our caravan.

Caravan used 1st 2 weeks of June in Scottish Highlands - no problems at all.

Used again 1st 2 weeks of August in Gargrave (near Skipton in N. Yorks.) and a dark(ish) grey stain has appeared in our melamine mugs and in the kitchen sink. It is not apparent on any other plates/bowls (also melamine) nor has it appeared in the other sink, or in the shower unit (although the shower hasn't been used that much).

The mugs have been stained by the usual tea/coffee stains and cleaned with Puriclean as was the water system: in both instances this was before the June holiday.

One thought is that the Gargrave water is, I'm told, quite hard whilst the Scottish water I think is quite soft. But we've been to Gargrave before with no ill effects.

Another thought is that the same bottle of green Fairy washing up has been kept in the caravan for a few years now. Can it have deteriorated? In which case why aren't the plates & bowls stained?

Any thoughts?

Peter G. Shaw

larry phelan 120/08/2021 16:08:40
1095 forum posts
14 photos

Could be due to an infected Haggis getting revenge.

Other than that I dinna ken.frown

Steviegtr20/08/2021 16:35:23
2244 forum posts
311 photos

I guess there could be a lot of iron in the Gargrave water. Cannot explain why it's not effected everything though.


Dave Halford20/08/2021 17:06:45
1757 forum posts
19 photos

Tea has tannin in it. Iron and tannin = blue black like steel nails or screws in oak.

Tim Stevens20/08/2021 17:33:37
1470 forum posts

Pottery and porcelain have a different chemical structure from melamine - glassy rather than plastic. So, it is likely that whatever the cause of the stain, the effect on melamine is likely to be different from more conventional (less 20th century) eating ware. Just a thought.

There is a lot of limestone around Gargrave, and hard water is known to leave deposits here and there. If it happens very regularly it produces stalactites and stalagmites. So look out.

Regards, Tim

pgk pgk20/08/2021 18:46:21
2324 forum posts
293 photos

Periods either of prolonged drought or of heavy rain can both lead to water supply contamination.
If it is due to hard water then a vinegar soak should shift it.


Rik Shaw20/08/2021 18:55:17
1458 forum posts
396 photos

I have just glanced through the results of a study entitled “The Pathological Effects of Melamine and Cyanuric Acid in the Diet of Walking Catfish” in which it records that said catfish fed on a diet of cyanuric acid and melamine displayed skin darkening (staining) within three days.

I would not suggest for one moment that cyanuric or even uric acid is finding its way into your sink - but if it - is this might explain the staining on your mugs.


Peter G. Shaw20/08/2021 21:12:06
1314 forum posts
44 photos

Some answers.

As far as I know, all the mugs, plates & bowls are melamine. They even have the same pattern on the outside. I assume therefore that they are all the same material. Incidently, we also have some "plastic" glasses. I say "plastic" because I don't know what they are made of, except that they are visually clear and lightweight. No staining on these.

The kitchen sink is also "plastic", but I don't know what sort of "plastic".

I'll try the vinegar soak idea tomorrow - if we've enough that is - and report back.

Cyanuric/uric acid. Don't know how to prove that.

Iron in the water. There is a rather funny tailpiece about that. Unfortunately, I am on chemotherapy, and have been for 2 years now. Starting from 2 years ago, my haemaglobin level has gradually dropped such that the medics are now somewhat concerned and rather comically the last 6 readings have been 113, 111, 109, 103, 106, 113. That last reading was taken the day after we came back from Gargrave. Which makes me wonder!

Oh, & by the way, yes we do have a reasonably quantity of tea!

Many thanks for the thoughts, I'll report back.

Peter G. Shaw

Howard Lewis20/08/2021 21:23:58
5348 forum posts
13 photos

If gentle methods fail, try bleach (Sodium Hypochlorite ) removes tannin stains from tea pot and mugs very well!

You only need a few drops to roll around and the stain disappears almost before your eyes.


duncan webster20/08/2021 23:45:40
3526 forum posts
63 photos

The stuff used for cleaning false teeth is reputed to shift tea stains and not leave everything tasting of bleach. Can't vouch for it as I still have most of my own gnashers

Peter G. Shaw24/08/2021 09:35:54
1314 forum posts
44 photos

Final (rather late) update.

Vinegar didn't touch the mug I tried it on, but since we were considering replacing them anyway (something like 25 years old, and one had splintered somehow internally) it's no real loss.

In respect of the sink, I used a cream cleaner originally from ASDA but really quite ancient (I believe it came with our previous s/h caravan, so could be around 25 years old) and along with a modicum of elbow grease, the stains were mostly removed. What's left is ok as the sink is not a single colour, but rather a faint mix of light colours. So thankfully, all's well now.

Thanks for all the thoughts.

Peter G. Shaw

p.s. Duncan, I do have a set of false teeth, and when I was given them (it) I said to the dentist "I suppose that means getting some Steradent now." The reply was "Oh no, don't bother with that, just use ordinary toothpaste - it's plenty good enough!" So that's what I've used ever since.

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