We are tested compatible with Effetre clear (product #004) since it is the largest volume “104” soft glass in production at this time. We use Polarimetric strain testing to ensure that there is minimal strain between our colors and Effetre clear. Polarimetry gives us specific data regarding strain in psi between two fused samples. We believe this is the most accurate measure of compatibility. COE (dilatometric) testing does not guarantee compatibility and can produce data with margins of error ( +/- 2) that are equal to the acceptable tolerance ranges (+/- 2). To read our article “One Manufacturer’s Perspective on Compatibility”, which you will find on our Tutorials page (under the Information tab above).