You’ve seen geodes on display at museums, art galleries, and jewelry stores. They are mineral or crystal clusters that are found inside certain rocks – amethyst is an example – and they are beautiful in their composition and clarity.
Martha Stewart created some of these faux geodes – and between her talented team of artisans and professional photographers, they looked AMAZING – but that’s Martha – almost too good to be true…
I had to try and make my own faux geodes with the kids to see if this experiment really worked.
First thing you should know is that alum is a salt – a pickling salt to be exact – so while it tastes horrible, it is safe for children to use.
- 1/3 cup Alum powder (found in the spice section of your grocery store)
- small containers – ideally egg-shaped
- white glue
- paint brush
- 2/3 cup water
We tried two versions of this – one with these shiny plastic Easter eggs and then a second version with an actual egg-shell (make sure all the membrane is removed from the lining of the shell). The egg-shell did work better, but is more work and very fragile – so do whichever you feel will work better for your child.
First paint a thin coat of white glue to the interior of your egg-shell/plastic egg and over the edge. Then coat with dry alum powder. This creates the foundation that the faux geodes crystals will eventually be drawn, and adhere, to.
You’ll want the glue to be completely dry, so leaving this for a few hours, or even overnight would be best.
Later on, or next day – whichever your case may be – pour 1/3 cup of alum powder into 2/3 cups of water and heat until boiling.
You want the alum to dissolve into the water and “super-saturate” the liquid. Keep adding alum powder into the boiling water until it no longer dissolves. You’ll see a bit of alum powder settle on the bottom of your dish even after stirring thoroughly – that’s how you’ll know the liquid can’t hold any more.
Place your eggs into a container just deeper than the height of the egg itself.
Carefully pour the super-saturated liquid into the container and make sure that the eggs are completely submerged.
If you want coloured crystals on your faux geodes, add a few drops of food colouring to the liquid. We (mistakenly) added two different colours of food colouring to one dish thinking they would settle into each egg. Instead they eventually muddled together – so I suggest just adding one colour per dish.
Leave your eggs/ faux geodes to grow overnight.
This is what you’ll find the next morning! (the egg-shell soaked up all the food colouring and the crystals none? That’s science for ya’)
The plastic egg did accumulate some crystals, but not as many as the real egg-shell…. BUT, because the plastic egg was coloured, it appears that the crystals are as well.
In an attempt to create “rubies”, I did add a bit of food colouring to the geode the next day. The longer you leave it in the solution, the bigger the crystals will become.
This one still needs to dry out a bit more – but isn’t it gorgeous? You can just see in the above photo how the crystals in our faux geodes are reflecting light on their facets.
Warning: these faux geodes are a bit fragile and shouldn’t be man-handled too much. If you want your crystals to last, I’d suggest a light coating of spray varnish to harden them into place.
This is a great experiment for kids. I’d even go so far as to suggest this as a science fair experiment.
Have a great one!