Page rank Evaporation.

In PageRank algorithms, some or all of a document’s PageRank may be distributed to the rest of the documents in the collection. This is called PageRank Evaporation. When the links with nofollow attribute, will not be getting anymore link juices to flow and follow the links on the page. Instead, the PR will be wasted and evaporates into nothing which should have been passed.

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PageRank sculpting is what SEOs used to be able to do with a site.

For example, if a page has high page rank and 3 outbound links to pages A, B and C. It used to be possible to "no-follow" pages A and B so that 100% of the link juice went to page C.

However if you watch the Matt Cutts videos he talks somewhere about how Google changed their algorithm to effectively reduce the incentives for PR sculpting. Now, in the same scenario, A and B would still receive nothing thanks to the "no-follow" but page C would only receive 1/3 of the page juice.

The remaining 2/3 pf the page juice "evaporates".

Page Rank is a SEO and website owners misunderstood. At one point in time page rank all the important functions was to define where you want the search results. It was all the calculations, a measure of the importance of the site.

Page rank evaporation is common when doing PR sculpting. This is when links with nofollow attribute, will not be getting anymore link juices to flow and follow the links on the page. This will make the pr to be useless and just go off.