I have some recipes for stepping stones but I haven't tried them out myself so I hesitate to recommend them.

I do know one way to get a perfectly smooth stepping stone that I have done myself. You could hold off using the ingredients you have and use them on another stone, but for this one, if you want to make sure it's perfectly smooth, you could buy a box of Diamondcrete. The last time I used it, I found it at Hobby Lobby and it was about $10.

You grease the mold with Vaseline or mold release, lay your paper pattern down, face down, cut a piece of clear Contact paper to fit, lay it down sticky side up, then do your mosaic using the indirect method, (the backs of the tiles all facing up), pressing firmly to the Contact paper.

Then you mix and gently pour the Diamondcrete. Follow the instructions on the label. It is super important that the mold is sitting on a flat level surface when you pour. The finished stepping stone will be completely smooth. You eliminate the need for grout using this method. It is more expensive than the usual method, but I used it when I had some commemorative stones to make on commission and they had to be smooth.

How you lay the pattern face down is, you first hold it up to a window or on a light box, and you transfer the pattern to the reverse side of the paper, using a bold marker. That way, your pattern is reversed, your tiles are reversed, and then when you flip the stone over, everything is right side up.

If you still want to try the recipes I have, let me know and I will post them.

Thanks for your response. I'd be interested to know what recipes you've found.
Thanks!

ONE. Durable and waterproof concrete stepping stone
5 parts Portland Cement
1 part Acrylic admix or concrete bonding admix
1/4 part poly fibers
1 part latex paint
Water as needed to make a paste like thick mud.
Option: replace 1 part Portland cement w/ fine sand.
Adding some fly ash or silca fume will make it stronger.
You can add colored latex paint to white Portland cement.

TWO. Smooth concrete stepping stone
1 part Portland cement (sifted)
3 parts fine sand (sifted)
optional: concrete dye colorants
Enough water to make a mud-pie consistency (peanut butter)

A form or mold of sort with removable sides (such as a medium-size pizza box)
Bucket of water
Sponge to wipe surface.

These are the two recipes she sent me. I guess the first one is more durable than the second one? I'm not sure but I think that's probably correct. She also told me that making stepping stones is a good way to use up old latex paint; just add some to the mix.

One day soon I will try out these recipes. If you do decide to use them, please come back and tell us how they turned out.

Slow's recipe for a stepping stone. Mix three parts of the sand w/one part Portland cement w/enough water to make it not quite soupy. Pour into a mold about half the depth of the mold. Put a layer of chicken wire in to ensure its strength, then finish filling the mold. Let harden overnight. Turn it out of the mold, then use your stained glass to make your mosaic, using Mapei Porcelain Tile Mortar for the adhesive and Mapei Keracolor grout to grout it. It w/stand up to any kind of climate. If the grout you have is cement-based, it w/work. For any outside projects, it must have cement-based adhesive and cement-based mortar to withstand the elements. The Porcelain Tile Mortar is the new product that replaced Ultra Flex II. These products are available at Lowes.

or would any paint do? (like the leftover paint after painting a bedroom)

The leftover paint from painting a bedroom is likely acrylic latex. Oil-based paint should be disposed of as a hazardous material. Latex-based paint is non-hazardous. Myself, I would only add latex paint to stepping stones.

How I would determine whether or not to use leftover paint in a stepping stones recipe: If the cleanup from painting is soap and water, then it's okay to use. If the cleanup from painting involves a solvent, then I wouldn't use it.

I have made a lot of stepping stones, but to get a really smooth stone, and WAY easier than trying to mix your own, buy a bag of Vinyl patch (cost about $12 for a 25 lb bag). All you add is water. Very strong and super smooth. I wouldn't use anything else.

Wow, super information! I will try this if I can find it. I haven't heard of this before.