Sorry for the delay in replying!

The two strength tests I do are the “bend test” which you asked about, and also occasionally a “tension test”.

Bend Test

For the bend test, I start by making all the samples to be tested the same size and thickness (unless I’m testing the strengths of different thicknesses, of course!). These samples might by made from different clays, with or without various additives, or might have been cured at different temperatures and for different times.

For the curious, my test samples are typically the same size and thickness of my colour chips, only without the hole for stringing. The cutter I use is a “squoval”, basically a rectangle with rounded ends, 40mm long and 28mm wide. I roll the samples at #3 on my pasta machine (which has 9 settings, #1 being the thickest; #3 is 2mm thick when measured by calipers).

Then I take a pair of nylon jaw pliers, put a sample into them lengthwise so that the pliers go half way up (I’ve made a mark on the pliers to show where to line them all up, since my samples are always the same size) and close the pliers so that the sample is firmly gripped. Then I the fingers on my other hand to bend the loose end of the sample all the way to one side as far as it goes, then all the way to to the other side as far as it goes that way, and so on.

I firstly count the number of bends it takes for the sample to develop a visible crack on the surface, then keep bending and counting until the sample is broken all the way through. (Although I get bored with counting after about 400 bends and generally call anything that survives 400+ bends “strong enough!” LOL)

Tension Test

This one takes a bit more setup and a bit more equipment.

The samples are a bit more complicated for this test. I’ll start by cutting out the same size pieces as above from the uncured clay to be tested (40mm x 28mm squovals at #3 or 2mm thick), but for each sample I also cut out 4 small ovals from the same sheet of clay (I use an oval Kemper Kutter, 18mm x 13mm). Then I put the small ovals cross-wise at the very ends of the squovals, so that ends of the squovals are sandwiched between the smaller ovals, and the middle of the squoval is a single layer of clay.

I put the samples on a tile to cure, with a foil-covered strip of (cured) scrap clay down the middle to provide support to the single-layer middle of the samples while they cure. After the samples are cured and cooled I drill a hole at each end, through all 3 layers of clay; I use a 3mm drill bit.

To perform the tension test, I have two pieces of stiff steel wire, each bent so that it can be threaded through a hole in one end of a clay sample. One piece of coathanger wire is relatively short: I hang this from the framework of my workbench. The clay sample to be tested hangs from that. I then hang the second piece of steel wire from the clay sample, put a cushion on the floor underneath the whole lot, and then hang successively heavier weights from the second piece of steel wire until the clay sample breaks (hence the cushion; some clay is strong enough to require a lot of weight to be added before it breaks, and I don’t want to damage my timber floors even though they are fairly tough!).

The ends of the sample are reinforced (3 layers thick) to minimise the chance of the wire tearing through at the end. (That would actually be a third test, although it’s not one I actually do that way.

Other Tests

I sometimes want to test the strength of clay that’s already been formed into beads and cured. This is generally not a particularly scientific test, but just to see if the beads are strong enough for me to consider them good to use. It also normally damages or even breaks the bead tested, so don’t do this if you can’t spare one! And finally, the way I do it is a bit physical, so if you have a bad back or problems with your hands or arms you probably want to avoid this… or at least adapt it (you could use a similar approach as in the tension test above).

What I do here is take two lengths of beading wire, feed both of them through the bead hole, and then tie or simple hold each length so that it forms a loop (that is, you end up with two separate loops of wire, each running through the bead hole). I have a junk roll of tigertail from when I started beading, before I knew that it kinked and proper beading wire didn’t, and tend to use that.

I then take something in each hand to prevent the wire cutting into my fingers and pull the two loops apart, sometimes like I’m using one of those slightly ridiculous chest-expander exercise thingies, sometimes by putting my foot through one loop and using both hands to pull up on the other. If I can’t break the bead that way, or if I can only break it by applying a lot of force, that batch of beads is good to use. ;)

Since this test applies force to a small area via the beading wire you’ll probably find that even with good/strong clay beads the wire cuts into the bead around the bead hole. With weaker clay, be prepared for this test to entirely cut the bead in half! (You can use the halves the same way you would cabochons if you want to, however, so it won’t be totally wasted.)

So there are a few ideas for testing clay strength. I hope they help!

Sue

I believe that Craftsmart is just the No Name Brand that Polyform makes for the Michaels Stores. Your best bet for something like this is to go to Polyform directly. You can reach them online at sculpey.com and at Polyform’s page on Facebook. If you do hear back from them, make sure to come back here and let us know what you found out. I am sure there are others who would appreciate the information!

If your question was relating to food safety / compatibility, I agree with Anna that the Craftsmart brand is not a product you should be using around anything edible.

Anna. Des Moines, Iowa.