I found an article on urethanes hiding in my computer and it may contain some info that the OP was asking about so here it is:
Just Paying Attention By Mark London
What about this Black Hammer ball and what makes it so special. This ball would either be first of second on everyone's list, simply because it pioneered a new design feature. Besides being the first $100 retail priced ball, it also had a kerosene smell. This was the first center-heavy ball on the market. Applying more physics principles, this ball was the first to tinker with the untouched inner workings to help produce a desired reaction. Balls to this point were all cover heavy or neutral at best. What was also unique were two markings, a center of gravity and a riser pin. The center of the bullseye marked the CG, but the riser pin was more difficult to find. In the first few batches, the pin was right on top of the bullseye. Then we heard a few of the balls would not work for lefthanders. Bowling 'urban legend' says one of the pins holding a ball along the assembly line fell, bending the stem. This put the riser pin in successive balls from this mold in a 1:30 direction from the CG, essentially placing the riser pin under the ring finger of a right-handed bowler. What was discovered by an attentive ball driller was to put the riser pin under the left-handers ring finger and ta-da: it rolled just as good for southpaws. Second on this ball was the urethane cover. It was very porous, especially in its out-of the-box chalkboard look. The only problem was after about 200 games, it was done. Resurfacing this ball was easy, it did not take very long and looked brand new. Unfortunately, the ball still reacted like it did before the resurfacing. The urethane was so porous, but yet those pores seemed to get compressed with more use, not allowing out-of-the-box traction. The second ball, the Red Hammer, although it hooked more, had a simliar urethane composition. That was corrected with the following Hammer balls.
So what happened to Columbia? After urethane was introduced in '81, they did tried various balls with different polyester compositions without a real breakthrough like the Yellow Dot ball. Then came the 1986 introduction of the Black U-Dot. Their first urethane ball had its drier lane companion, the Wine U-Dot, but the Black U-Dot was the ball every style could handle with ease. Crankers, tweeners, and straighter players loved this ball as Columbia got back a lot of their bowlers who loved the Yellow Dot from a decade before. Pete McCordic and Bob Benoit rolled their TV 300 games using this ball. AMF had also supplemented their Angle line with a newer ball that did something no one ever thought was really good. The Ultra Angle's core allowed it to roll over a fresh part of its cover each full revolution down the lane. Most who saw this were skeptical at first and many drillers tried to drill the characteristic out of the ball. They may have reduced it, but not eliminated it completely. Track flare helped the ball hook more and helped the tweeners and straighter players compete with the crankers, who were running away and hiding from most of the competition. This, like the Yellow Dot, was another ball ahead of its time. Brunswick was not left out at this point, either. Assisted by a print and TV commercial campaign and by signing Mark Roth away from Columbia, the Rhino series of balls helped put the big "B" back on the ball map with a slightly different reactions for each cover color.
Meanwhile back at Hammer, another one of the great balls for every style was the dull Blue Hammer. It offered the same core design, but a stronger cover compared to the Black and Red models. Whether your preference was for polished, dull, label drill, or off-label drilling, finding one who did not like this ball was hard to find. It was one of the first center-heavy balls that rolled great from extreme inside angles, crankers loved that. You could also play outside and still get the ball to finish, tweeners loved that. On short oil patterns of that time, the pearl versions, either Blue Pearl or Red Pearl were popular as well, with the Red Pearl usually the first choice. In any case, same Hammer label, same Hammer hitting power.
The last great urethane ball was Ebonite's Nitro. Ebonite did alright with its first urethane ball the Firebolt, but had designed a new cover material which was advertised to have a wider footprint on the lane. They also put together one of the first traveling seminar shows to advertise its prowse, as well as answer general pro shop questions. This ball did not disappoint either. Sales did not hurt as Walter Ray Williams, Jr. used the ball on many of his telecast appearances, which were becoming more frequent like Roth had in the late 70's.
By the late 80's, as more and more balls were being released in a much tighter time frame than before (four years the ball marketing lifespan for a given ball at this point), some felt market saturation was being reached. Regular ball purchasers were given the monicker, "Ball of the Month Club" members. Technology then was progressing faster than before, but keep in mind, not nearly as fast as it is today. The next big step was a new urethane cover than blew everyone away, including a small ball company.
The Nu Line Xcalibur looked from a distance like a Yellow Dot, but as we soon found out, reacted like anything but a Yellow Dot. The ball seemed to skid forever, then make a left turn no one had even seen before without a different release. If you are old enough to remember seeing Star Wars in the theater for the first time; yeah, that feeling. Once Marc McDowell threw it during his 1992 AC Delco Tourney win, the reactive resin era had begun. Pro shops all over America received calls during the show about this ball that few knew about. Nu Line was over whelmed with orders in the following weeks, it couldn't keep up. The handmade balls were soon gone, and Nu-Line contracted Columbia to manufacture the ball. At the same time, Brunswick had broken down the cover formula and was set to come out with one of its own. The Purple Rhino Pro was a great seller and performer in its own right and appeared on TV finals almost every week. TV finalists were standing further to the left creating angles at the back end of the lane unlike any ever seen to date. One other thing we did notice were weaker releases began to work with these balls as lanes got drier. We could roll them faster and still get wild pin action. If we slightly sanded the cover, we could tone down the snap for the cranker style, allow him to manage his roll better. What's up with that?
And so this chapter ends. There, of course, are couple more balls on the list. But with more ball introductions in less time these days, those really great balls aren't around as long anymore. At this moment in 2006, the trend is stronger reactive resin covers on asymmetrical cores. Next year who knows? It will probably be different again, like it was in 1996, and before that in 1986, and before that in 1976.
