Ever wonder how we came to use slats for measuring how we roll out clay? I guess we had to have something to give us a guide for thickness prior to firing. Playing cards are handy and inexpensive, right?
Even though they are cheap the card certainly can get boring and frustrating. You'll quickly find out that the playing cards slide all over the place, get dirty, can't be washed, and stacking up cards is tiresome. The plastic slats have really been an efficient and easy way to guide the thickness, and they can be washed!
I was further curious about the slats after a customer contacted me regarding our plain white slats versus Pam East's colored set of slats. WLW came up with the white standard plastic slat 8 years ago when I wanted something to give to students that could be washed and easier to work with. For basic pieces and classroom use, this slat is perfect. Especially for beginners who don't know how much they sand off or their piece needs to be a little bit thicker to compensate for engineering.
So out came the digital calipers, 3 decks of standard playing cards, Pam's Set, and our White Slats. I measured and remeasured. I didn't make the assumption to take one card, measure it and multiply it by 2, 3, 4 etc. Even by pressing the caliper closed firmly, the measurements came to more than 2x, 3x, etc. This can be attributed to air etc. It was a lot of measuring! For the standard card measurement I used the Las Vegas standard decks in red and blue and measured both.
What I found is the following:
Not included in the chart was Cool Tool's Rolling Frame #4. My digital caliper registered .98mm, which would not quite be a standard 4 card thickness, even though it is marked as a 4.
How about other things that effect the thickness? Imagine that a beginner does not press down firmly when they are rolling or that you chose to use glue or tape inbetween the cards. This will effect the thickness as well. The brands of cards and material will effect the thickness.
So keep in mind that whatever you buy is really just a suggestion. Get to know the pieces after you fire them as to whether the card you used was the right thickness. It's just a starting place. It's not a hard and fast rule to use 4 cards or 5 cards. There are too many factors that come into play. Keep a recipe card to write down what you used and then evaluate the pieces after firing.