a lap is needed during polishing because glass on glass lacks the degree fluidity of pitch which is needed to polish the mirror smooth.
Tempered Burgundy comes in the Willmann-Bell kits and is made from pine trees. Googluz is a petroleum product and is recommended by the Stellafane workshops:
I used Tempered Burgundy till it was to hot in the summer then I used hard Googluz and then when it got cold I used soft Burgundy. The top picture is a well maintained, channeled lap whereas the lower is a poorly maintained recipe for bad contact.
The upcoming lap making photos were taken at a Stellafane workshop.
