Sodium has a strong effect at a concentration of 0.01% The concentration should not exceed 0.02%, as this leads to overmodification due to the formation of the AlSiNa compound. However, sodium modification fades quickly (within 20 minutes) due oxidation and reaction with the melt. Degassing or melt agitation can impair the modification as well. A typical range is 0.007 to 0.012%.