Rust inside a Thermos

[Drawweight]

I left a quite expensive stainless steel flask in a hotel room. I phoned them up to ask if they had found it and if I could pay to get it shipped to me. However the hotel just said they’d send it to me (Highly recommend the Warwick Castle Hotel)

Unfortunately it was quite a few weeks before I got it and it must have been left on its side with a bit of water in it because it has a faint rust line down the inside.

I don’t think it’s penetrated into the body itself, just very much a light surface mark.

Is there any way to remove this? I’d struggle to actually get anything in the neck to scrub it.

[Bill]

Put something loose and abrasive in and shake it about. Sand doesn't seem right, but iirc walnut shell blasting is a thing...

ETA Google says I'm not making it up!!

[breamster]

Scouring pad moved about with the handle of a wooden spoon?

[LooneyTunes]

Decanter cleaning balls might shift it?

[Simpo Two]

Which bit of the inside of a thermos flask is ferrous? I thought they were silvered glass. Or is that just old ones?

[Saleen836]

Bill said:

Put something loose and abrasive in and shake it about. Sand doesn't seem right, but iirc walnut shell blasting is a thing...

ETA Google says I'm not making it up!!

Egg shell should work

[OldGermanHeaps]

White vinegar should eat the rust.

[B'stard Child]

Simpo Two said:

Which bit of the inside of a thermos flask is ferrous? I thought they were silvered glass. Or is that just old ones?

Err that was the old ones silvered glass in a plastic body OP stated

Drawweight said:

I left a quite expensive stainless steel flask in a hotel room.

It's the air gap that stops the heat loss matters little what the constuction method was

[SlimJim16v]

OldGermanHeaps said:

White vinegar should eat the rust.

Or a solution of ascorbic acid, vitamin C.

[sherman]

Either buy this go to your local nice pub and ask if they have a scoop of renovate powder. Put the powder in a full flask of warm water and leave to soak overnight. Rinse very thourghly with lots of clean water.

https://www.dunelm.com/product/astonish-premium-ed...

[ARHarh]

Simpo Two said:

Which bit of the inside of a thermos flask is ferrous? I thought they were silvered glass. Or is that just old ones?

I guess by the fact he said it is stainless that it is made from stainless steel. Anyhow if I had bought an expensive stainless flask and it went rusty I would need to question the quality of the materials involved in construction and whether it was really worth the expense.

[loskie]

Milton sterilising fluid tabs or a strident tab in it

[B'stard Child]

ARHarh said:

Anyhow if I had bought an expensive stainless flask and it went rusty I would need to question the quality of the materials involved in construction and whether it was really worth the expense.

Stainless steel is no guaruntee of rust free - Most fittings on boats are stainless steel and will rust but just require a polish to remove

Correctly treated (Passivated) so a combination of a citric acid solution soak and sodium hydroxide soak creates a much more rouging resistant surface

(At work we mix qtys of saline solutions in Stainless Steel tanks up to 44,000 litres - rust on solution contact surfaces is not acceptable)

[Joe5y]

Toilet brush?

[B'stard Child]

Joe5y said:

Toilet brush?

[Countdown]

What about a baby's milk bottle brush?

[Lotobear]

Just get some simple citric acid crystals from your local hardware shop (Wilkos was good when it existed) and put a heaped teaspoon in with some warm water and leave overnight then rinse. Job done.

....I've used this for engine block water jackets on numerous occassions, at a much stronger solution, and they come up like a new casting.