Monday, 24 February 2014

Making chalk

Please read this post fully before you start making chalk, including the safety information on your plaster box

If you're anything like me, you just don't know what to do with that left over Herculite craft plaster you bought from hobby craft last year!  Ok, maybe that's just me.  I bought some to use to make fossils in the sand but never got around to it.  Then a few weeks ago I had a go at making crayons, they went well.  Then I remembered I had seen someone had made chalks from scratch too - Eureka!

The following recipe is for Herculite II plaster which you can get from any hobby craft or larger hobby store.  I have measurements for other plasters at the bottom:

1) Get your Herculite II plaster (I used a 1kg bag), a measuring spoon or cup, an empty mixing jug, a spoon and some water (cold).  
2) Lay down an old towel or sheet on your table (because this is a messy job).
3) Measure out 2 parts plaster to 1 part water (I added food colouring to each part water every time).  Use any size spoon but make sure you follow the ratio, I used a 1/4 cup because that fit in my mould perfectly.
4) Mix like crazy!  You're after a smooth consistency without any lumps or too many air pockets.
5) Pour carefully into desired mould (I used a cake mould I found in Asda on offer!)
6) Wash all used apparatus and repeat steps 3-5 until you've made enough to fill your moulds.
7) Leave to set for 90 minutes (depending on thickness).  I found that if I used regular water based food colourings then anything yellow tends to set within 30 minutes, followed by blue and green in 45 minutes.  My red took over an hour to begin to set. The plaster is exothermic as it sets, always fab to feel like a scientist. 
8) Pop out of your mould and enjoy!

Psst:  The boys will really get into mark making if you make in a favourite shape.  I used trains, but Asda also had a dinosaur mould.  Try anything to get them excited!

Safety tips for using Herculite plaster:

Always research the plaster which you use before you start.  I didn't make my chalks near children as plaster dust is quite dangerous.  If you inhale it can cause certain problems and can cause irritation on the skin.  However once mixed and set it should be perfectly safe to use (just don't eat it!).

Ratios for different plasters:

Fine caster plaster (very common but softest type of plaster): 2 part plaster: 1.25 water
Crystacast (less common but very hard): 2.5 part plaster: 1 part water.