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Woo Hoo!! Its that time of the year again, making up this agar. What does everyone make it up in to get the various depths required?

Help Lorrae

I use a 10-dropper tray with the divider removed to set the agar. Gives nice sharp corners and a depth of 3cm. I tape some graph paper under a sheet of perspex for cutting the set agar.
I like to make it a really strong colour, so fading isn't a problem. Here's my recipe:

PINK/PHENOLPHTHALEIN AGAR BLOCKS

For 1 block (10 dropper tray, divider removed)

14.4g agar
480ml water
24ml 1M NaOH
4.8 ml phenolphthalein

Put agar in beaker, add water and magnetic stirrer. Full heat, stir to dissolve. Remove stirrer, continue heating till boiled. Remove from heat. Add NaOH and phenolphthalein. Pour into tray, allow to set.

If you have any problem with fading - make sure you cool the agar to below 60 deg C before adding the NaOH and phenolphthalein.

We don't have anything as smart as dropper bottle trays so I have used 3 litre ice cream containers. These also have sharp edges. We invert the block onto a large flat white tray and then the teacher chops it into smaller blocks for the girls to hack away at.

We use 0.1 M H2SO4 for the solution. If you need a faster reaction make the concentration 0.2 M.

Robbie

I use dissection trays I find they work well
Make sure you cool the agar a little befor adding sodium hydroxide. & Phenolphthalein
Noona

I use takeaway containers, fill them to a bit more than 3 cm and cut the blocks into thirds. The kids then do the rest to get their 1, 2 and 3cm cubes using rulers and scalpels.

In all the years I've been making this stuff I've found that the colour develops better the longer it's kept. I set it in an enamel tray. I don't refrigerate it as in the past have found it will turn a murky purple grey colour instead of the bright crimson colour; still gives the same reaction though. Has anyone else noticed a colour change in the fridge. We weren't sure if it was due to "old phenolphthalein" but as I said the reaction still worked.

Thanks for all the suggestions. I've tried the dropper bottle trays and put in an overhead photo copy of some grid paper on the bottom to make it easier to get the size. I had been using take away food containers but didn't like the dent in the bottom of them. I have made up a 0.5cm, 1cm and 2cm trays. I will keep you posted.

Thanks again
Lorrae

Mine always goes the murky purply colour even before I put it in the fridge. I wondered whether it has something to do with puting the NaOH in at the wrong temp, instead of after the temp goes under 60 deg. That's what I am going to try this time, anyway. But as you say, it still works, just not as pretty.

I have definitely found a big difference in the colour depending on when you add the NaOH. Add it after the agar cools below 60 deg and no need to put it in the frig. It should be fine then.

Robbie

I am a little lazy ...
I make it in ice-cream containers.. then cut it into cubes after it has set... I had so much trouble getting the right size containers, then I found the agar shrunk after cooling... so now I just bung it in above the level I want, when it's set I turn it out onto a copping board and using a sharp knife and metal ruler, I cut it.

I tried leaving the very first batch I made out on the bench overnight to set. Got in the following morning to find an army of ants munching their way through every tray I had made. It now goes in the fridge and teachers just have to live with any colour variation.
Lyn.

The agar gel I made was fantastic.The colour was great and the grids in the bottom made it so easy to cut to the correct size. All im all it was very successful. Thankyou all for the great tips. It always makes the job easier.

Lorrae

just thought i would thank all those who put onto this thread - it has been so long since we did this prac i had forgotten a lot of the hints so did a search found this thread and have got a list of great tips


thanks labbies for your help from the past and always the present

Hi all,
I would also like to thank you for all the help. I was just asked to do this and I was looking for the recipe and here it is , just in time
Lada

Hi Xenon

When you use the 10-dropper-bottle trays to set your agar, do you have a trick to getting the agar to come out nicely? Mine sticks to the plastic sides and refuses to come out, or sometimes half of it comes out and makes a big mess.


Thanks
Tina

I use the dropper bottle trays as well. One with the dividers IN and filled to the top, and then one filled 2/3 and one filled 1/3 full (without dividers). I run a sharp knife or a spatula around the outside and they come out fine. Oh, I generally use double the amount of AGAR powder, so the cubes are quite strong and rubbery. (I guess that probably helps keep it all together!!)
Ian

Thanks for the tip, Ian.
I find that in hot weather the cubes are sloppy. I will double amount of agar powder.
Lada

After reading about that Gaur Gum I tried to substitute it for Agar due to cost of agar
Don't go there!

I have used milk or juice cartons for moulds. Cut out the base to low height required, for 1,2or 3 cm blocks. Measure the height with a ruler allowing a bit more for shrinkage. Relatively easy to unmould , using knife blade around the sides or /and pull apart , cartons are flexible. Place cutting board on top of mould and upend, and it falls out or a little pressure on top releases the block. Blocks are small so if one "plays up' no worries . Don't re-use or use old ones as the wax finidh deteriorates and they don't unmould as cleanly.

One version of the prac requires cylynders of agar. I use the tube from a texta pen cut open at both ends, and gently pushed through a block of agar, then a pen with flat end of similar diameter to gently push it out of the tube. A few failures but patience gets enough formed.

I have also used a wire cheese slicer to cut the agar, as well as a knife.

I'm going to put more agar in my mix too.

My thanks to all contributers
Rosalie (another one)

Thanks from me also - awesome idea to use the dropper trays!

I made a batch on Friday with tray dividers in, & this morning I turned one upside down, pulled the sides apart a little & out came 10 perfect pink cubes!

Chemtalk absolutely rocks!!