Australia's Science Forum

Hello! I hope you've all survived the first full week back with students!!

I am trying to make a block of blue ice. When I arrived, there was an ice cream container with beautiful blue ice in it for use in a fish tank to show convection. Said ice block has now been used and I am trying to recreate it ready for when we need it again and after my first attempt, the food colouring was all settled on the bottom of the ice cream container and even had a blowout underneath! So, for my second attempt, I used more food colour and stirred it as it was cooling down, breaking the ice on the surface etc hoping to have an evenly blue ice block... I have just checked it after being in food tech for 2 periods and then lunch. It has completely separated again and the surface layer of ice is now too thick for me to break. I can see an air bubble trapped inside the blue centre still moving around so it will be interesting to see if the base of this container has a blow out later or not. The block of ice itself is quite pretty but not functional for its intended use!

I feel so silly, but does anyone have any suggestions?

Not silly at all, it's a very common problem!

Someone told me that if you add salt to the water, the food colouring will not separate out. I haven't had a chance to try it yet myself, if you do please let me know if it works or not...

Is it possible that the Blue was copper sulfate and not food dye .

Cold filtering is a method used to separate particles out of solution .I guess thats what is happening when you freeze it .

Swimming Carnaval today .
Time for an experiment

Try making the blue water with either blue ink or blue paint and then freezing.
We use to have a powder die that use to work but have not done this for a couple of years now.

Just had a thought can you get Blue cordial and use that.

melsid wrote: ↑08 Feb 2021, 07:22 Not silly at all, it's a very common problem!

Someone told me that if you add salt to the water, the food colouring will not separate out. I haven't had a chance to try it yet myself, if you do please let me know if it works or not...

salt water did cross my mind... I'll have to give it a go!

bigmack wrote: ↑08 Feb 2021, 08:17 Is it possible that the Blue was copper sulfate and not food dye .

Cold filtering is a method used to separate particles out of solution .I guess thats what is happening when you freeze it .

Swimming Carnaval today .
Time for an experiment

blue.jpg

I'm sure if it was copper sulfate it would have been labelled. The previous lab assistant was amazing at having everything organised! Let me know how the experiment goes!

bigmack wrote: ↑08 Feb 2021, 08:17 Is it possible that the Blue was copper sulfate and not food dye .

Cold filtering is a method used to separate particles out of solution .I guess thats what is happening when you freeze it .

Swimming Carnaval today .
Time for an experiment

blue.jpg

That freezer is looking incredibly empty. You would swear you had had a huge clean up

Merilyn1 wrote: ↑08 Feb 2021, 10:31 That freezer is looking incredibly empty. You swear you had had a huge clean up

It's certainly devoid of Stinky Brains and Eyeballs Merilyn

OK heres an update after a few hours in the Freezer.

Methylene Blue is the worst , obvious separation of dye from the water and dark colour at the bottom .
Food colouring is the next worst , similar to Methylene Blue but not quite as Bad .
Both copper sulfates seem to be quite uniform but there is a blotchy /patchy look to them .
So far the winner is Food dye with salt in it .No obvious separation and quite transparent . I'll check in at the end of the day .

Well an interesting experiment .Salt seemed to be the best result but even then it was apparent that it was starting to concentrate as it froze .
Strangely the Methylene Blue turned Purple but when I touched the Beaker to wipe off the condensation , it cracked

I find it interesting that the food dye moves to the middle of the ice instead of creating a layer at the bottom. That's what it did in my ice cream container as well! I'm sorry about your cracked beaker. Thanks for doing the experiment though! Looks like I should add some salt to the water... I wish I'd paid more attention to how the ice looked before we melted it!

Well done Bigmack, that's just great

I added salt (probably a bit too much...) and an awful lot of blue food colour! It is a very dark blue ice block now

That's a great experiment. Thank you for doing it for us.

I put a few drops of Universal Indicator in the water and freeze. It's not blue, but it doesn't settle out like food colouring.

RosalieL wrote: ↑09 Feb 2021, 11:04 I added salt (probably a bit too much...) and an awful lot of blue food colour! It is a very dark blue ice block now

Cool Rosalie ,
I had a flash back ,
last year or before I remembered being asked to make some Blue Ice cubes.I also remembered having the same problem . Thanks to this ,I now know what they were probably wanted for and will know what to do next time .

I've just been asked for blue ice cubes for tomorrow, I've got them in the freezer now with the salt method.
Thanks so much bigmack for doing that last year. I remember reading it and had to go and find it.

Pleasure .
Actually you just saved me some work as I was asked for coloured Iced cubes for next week and I had forgot I had done this

after reading this thread last year during lock down I was making red and blue bricks for showing warm and cold water convection currents coming together in a fish tank...awesome.