RISO

Risograph inks are soy-based and do not conform exactly to any color standards. The listings below are approximates for reference only. Additionally, Riso inks are also slightly transparent and allow for variations in overprint and based on the color of paper they are printed on. 

Rubber band

This a common problem on RISO RP3100, the rubber band that allows the master to be removed breaks because of the deterioration of the rubber. 
I found an old explanation from PrntNow

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