very strong toilet clearer

No idea - but cracking it would be Really Quite Awkward so I err on the side of caution.

Theo

A thick piece of ceramic may crack more easily than a thin piece, because you'll get a greater temperature gradient across the thick piece, and hence greater mechanical stress as one side heats faster and expands quicker than the other. A thin piece of ceramic heats more quickly right through, so less thermal gradient and less stress. But it does also depend on the strength of the ceramic and it's thermal expansion coefficient. It's not simple.

I'm not getting the boiling water lark

are we just using boiling water because it's easer to dissolve the crystals

or does the temperature of the water on application matter

can't I just let it cool down before tipping it in?

I think I saw this in B&Q (a few minutes ago), in amongst other branded products

I left it there as I was looking for something more generic rather than branded, as that way I don't get fooled by the over optimistic marketing.

but they had nothing generic, and in absence of any recommendations for a brand, I left it there

Now I have a recommendation, I go back later and have another look

Thanks

Has the glaze gone? If it has and its in the porous part of the pan, probably nothing. However it might be embedded in lime scale, but only you can know. I guess the usual crowd will be along to suggest angle grinder or dynamite, but that would be silly. Wear shades when in the loo? Brian

surely the stain that I have is discoloured limescale.

so I need an acid?

I use phosphoric acid, it works quite well for a first soak and I finish off with washing liquid overnight.

even generic ones will have a maker.

But ether side of a thin glaze may still have high temperature difference across it leading to cracking of this protective layer. During manufacture temperatures are ramped up and down slowly.

Acids react faster if they're hot. Most people cleaning toilets just want to do the job and move on. If it's cold you have to wait longer - depends if you can leave it for a few hours, or if someone will come along and flush it away. Given there's already cold water in the pan, adding a small amount of hot will warm it up.

Stronger acids (HCl) work faster, but there's more risk of damaging the glaze because they're stronger acids.

Most of the time it's not a problem to use heat when cleaning toilets, I'm just cautious (although I've been tipping boiling water down blocked sinks since forever and not had cracking problems, so maybe not an issue).

Theo

Just paint the inside of the bowl to the same colour as the stain and claim it was an expensive designer item.

I meant a generic chemical

the problem with this category of product is that there doesn't appear to be a requirement to list ingredients

and many of them don't

They just contain marketing blurb

You can't tell whether, or why, they might work better than just squirting vinegar on the scale, at one tenth of the cost (which is what I do to descale my shower cubicle)

Well, it is interesting at the same time, certainly.

So follow it up with some caustic soda.

Brick acid turns limescale into soluble calcium sulphate, and caustic soda turns fat bergs into detergents and soaps. And turns brick acid into sodium (bi) sulphate

glaze is glass. Sulphuric acid comes in glass and ceramic bottles. It will not harm glaze at all

Chrome plating is another matter....

well in my experience you will have two things. Limescale and encrusted fatty turds and turd stains. Acid clears the scale, followed by alkali to saponify the fats and to bleach the organic stains

Any citation for that? Half a bottle per bend is actually fairly dilute by chemistry lab standards.

Bicarbonate of soda or washing soda is a lot safer to handle even if it will fizz a bit.

Brick acid is hydrochloric - calcium chloride is fairly soluble whereas calcium sulphate aka plaster or gypsum is only very slightly soluble.

Using sulphuric acid on limescale might flake some of it off but would leave you with flakes of gypsum.

Any idea what the stain is you seem to have tried the obvious things that would dissolve limescale or remove the colour at least if normal waste that goes down a toilet. It is possible it is a stubborn limescale deposit and more concentrated or longer exposure to acid may help. In our first grotty rented place the bottom of the toilet was damaged the glaze was chipped or worn and it looked greyish the owner replaced it eventually due to another problem.