The main ingredient in gunge is a food thickner. There are a number of options open to you.
If you are in the UK Natrosol HR250 (often mis-spelt Natrasol) from The Basic Chemical Company (see address below) is a good material. This is the supplier the BBC have used (not sure if they still do, but I wouldn't be surprised)- You will need to buy a minimum of 1 kg of the natrosol, but this makes a good gunge.
The Basic Chemical Company (UK) Ltd
Sands Industrial Estate
Ebay/ other websites
There are other suppliers that well sell you smaller quantities, either found on the web or through Ebay. Personally I don't believe these generally offer particularly good value, unless you only want to make one bucket full. It is likely (although I stand to be corrected) that these suppliers are selling on re-packaged Natrosol .
Xanthan Gum- this is sometimes available from the supermarkets (certainly Sainsburys) or health food shops as it is used as a gluten replacement.
Guar gum- another alternative that can sometimes be found in health food shops.
If you are in the US, you can use Methylcellulose (Methocel) from The Chemistry store- www.thechemistrystore.com or Ethylcellulose from Douglas and Sturgess- www.artstuf.com
Elsewhere you may need to find a local source for one of the thickeners.
The substances used to make gunge generally have long shelf lives (normally several years) and so can be bought in larger quantities and stored if desired. Moisture is their biggest enemy, so they will need to be packaged in a well sealed container.
You will also need
powder or poster paint
Suitable container to mix in- bucket for the quantity described
Wooden spoon, whisk, paint stirrer or similar
Step 1: Safety
The largest single issue is the slipperiness of the gunge- it can be very easy to slip over on. It is therefore essential to consider this when planning any activities involving gunge, including clean up and washing off as the most significant effects will be found on a smooth surface such as a bath!
Most of the materials are supplied as relatively fine powders, and as such create nuisance dust. It is therefore worth wearing a dust mask when handling large quantities. Likewise if this dust gets into eyes it can cause irritation so goggles may be appropriate.
Most of the materials are sold as safe for skin contact and to date I have not had any problems with this. I would however be slightly wary of allowing prolonged skin contact with the colourants as it may stain!
All of these main materials are not hazardous when eaten, however many are used as laxative additives, so it would probably be unwise to consume large quantities !
In addition to the specific information above, general safe chemical handling practice will further reduce the risk of any issues, in particular;
Store materials in sealed, well marked, containers in an area out of reach of children and pets
Wash hands before and after handling these materials
Dispose of excess/ used materials/ empty packaging responsibly
Wear dust mask when handling powders
Clean up any spills quickly- Avoid using water to stop the area becoming slippery
Do not use utensils/ containers/ cleaning cloths that will be later used for food
Supervise children if they are making the gunge
Step 2: Step 2- Prepare the Ingredients
Measure out the following quantities of materials. I use plastic cups or a jug to do this, but a piece of folded paper will work as well. Quantities do not have to be precise, but it may help you make a batch the same in the future if you can be fairly accurate.
The water can go into the mixing container straight away.
Powder paint 160 grams (2%)
Thickener 96 grams (1.2%)
HOT water 8 litres
There will be variation in the properties of the gunge, most importantly the viscosity (thickness), dependent on the materials used. It is therefore worth experimenting with small quantities first before you make a large batch, until you have a goo you are happy with. The quantities given in these instructions will work well with natrosol, and will therefore serve as a good starting point.
You will want to mix up in an area where a spilt mess can be easily cleaned up, so probably not your living room!
Step 3: Step 3- Mix
Start by mixing in the colouring into the water- 2% will give a good level of colour and opacity for most uses, but dependent on what you want to use your gunge for you may need to vary between approx 1% and 5%. Liquid poster paint (tempera) can also be used, but I wouldn't recommend food colouring as it stains easily.
Water must be hot for the mixing to work correctly. If natrosol is dispersed into cold water, the thickener tends to drop out and form a jelly that won't then mix correctly. I tend to use hot water straight out of the hot tap.
Add the powder into the water slowly whilst stirring thoroughly and keep stirring until you notice the water starting to thicken up. This will usually take a couple of minutes. Sieving in the
Leave the gunge to stand before using it. It will need time to cool, and as the viscosity slows convection, this will take a lot longer than ordinary water. For natrosol the mix will take about an hour to thicken up to full viscosity- I often leave it to stand all night. Other thickeners may need a different length of time
Step 4: Step 4- Using Your Gunge
It is possible for the gunge to stain, so keep away from soft furnishings and make sure any clothes that get covered are washed thoroughly and preferably before the gunge dries.
The gunge can be disposed of down a normal drain, but it is well worth diluting it with water first so that it flows easily and doesn't block your drains. If left to stand for a few days after use it well genrally break down to a watery consitency, which will aid disposal.
If you want to know more about making gunge, or messy games, visit my website: http://www.superpants.net