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I always use a extra strong phth brew. Just add some to a small amount of metho just before adding it to the agar. I also flood the top of the agar with phth once it is set. I leave this over night and then tip off any excess in the morning if there is any left. It does tend to absorb into the gel.

Thanks everybody. I am now a happy bunny and feel all ready for the next time we do phth agar. I used the phenolphthalein powder and it mixed in really well (I was worried it may clump). Fantastic dark colour. If it did fade it wasn't enough to stop it looking great and there were no layers. Will be doing that from now on. I used the equivalent of 1g per litre and had already increased my agar to 3%.

Seriously dude - time for some photos! If for no other reason, then to entertain those of us with cabin fever stuck at home, with no life at the moment!

The one on the left is the one made a few days ago now. The colour has really evened out a lot but is still patchier than it looks in the photo. The one on the right is with the phth powder, made yesterday. They have been together in a box overnight in the fridge with all their friends from the various attempts over the last few days!

I've had batches in both of those colours. And seriously, what does it matter as long as the little cherubs have the same start point?

Thanks for the photos, btw.

I have enjoyed re-reading this thread. Well done to you all.

Here it is the whole 8 page post on Our favourite topic with lots of tips on what to do and what not to do including tried and true recipes!!

worth bumping this up for the new members.

Well, it's that time of the year again here. Last year one of my teachers bought some of the silicon ice cube trays - they come in 3 sizes and work perfectly to give 3cm, 2 cm and 1 cm cubes (plus a bit in case they shrink!)
So easy to pour into the moulds, then turn out and give one of each size to the students to cut to exact sizes required. So much less waste too!!

Can you post some photos of the trays? The bit I am intrigued by is "one of my teachers bought..."
In the past I have used the unitrays, sometimes with the divider and sometimes without (that's a whole other post). This year, a new teacher wanted trays of 1cm, 2cm and 3cm depths - in the past I've just given the large ones and they have cut it up themselves. As I was time poor, I just used three trays, but there was a lot of waste. I'm interested in these ice cube trays. Any ideas where they came from?

Hi Merilyn1, I don't have any pics yet but I'll get some soon!

THe trays came from KMart and cost a couple of dollars each. We have 2 large grey ones with 6 holes in each, 1 of the medium blue one with 15 holes and 1 of the small red one with 14 holes - but it measures 2cm x 1cm, so the students use half a lump.

Here we go, finally remembered to take a pic of the trays we now use.

Each of the cubes is slightly larger than the size we actually want, to allow for shrinkage. We cut the red ones in half to make two 1cm cubes.

It took one 800mL batch to fill what you can see here.

Sweet Melsid . we had sooo much wastage last time . Love it .

Great thank you for sharing

That is so clever! I wasted heaps this year, this looks a great idea. I will be stopping in at the local K-Mart to find these!

So, I have an order for Phenophthalein Agar for Thursday, only to realise I don't have any Agar......so I am experimenting with gelatin.
Has anyone tried this?
I'll let you know if:
1. it sets and
2.it works (or not).......................

Or ask a local high if they can help??

I agree with Labbie - go on the bludge. The time you mess about with it could be time spent "networking". I have never tried or heard of anyone using gelatine.

I think you are pushing your luck with the gelatine. If you give the teacher something that doesn't work there will be no end to the complaints. Labbie's advice is good or just tell them that when the agar is ordered in then they can have their prac.

I did try the bludge option but agar is pretty expensive......so wasn't successful there.
I have made the teacher fully aware of the problem, I'm lucky my teachers are pretty relaxed, so she said if it doesn't work then she will just reschedule the prac when I have some