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Blogdowntown investigates: Sidewalk chalk

By Michael Katz
Published: Thursday, July 19, 2012, at 03:36PM


A week after chaos ensued at Chalk Walk, tensions are still running high between members of Occupy LA and the Los Angeles Police Department.

Blogdowntown recently spoke with Captain Horace Frank of the LAPD who explained why the chalking was such a big deal.

“I can tell you that based on my discussions with some of the … folks over at Pershing Square … it costs them money to pay to wash it off,” Frank told Blogdowntown. “It takes a considerable amount of effort to power wash … And we’ve seen the bills that come with [power washing] … You’re not just going to wash this off with a hose, because they tried it.”

The police captain added that even if the chalk was able to be removed with an everyday hose, someone would have to foot the bill for the time and money spent to do so.

Although the specific type of chalk protesters used last week is unknown at this point, we at Blogdowntown, in a non-scientific study, tested different types of street art tools to see how difficult they are to remove. We tested regular sidewalk chalk, soft pastels and oil-based pastels. Pastels are often used in street art competitions and provide a more permanent and colorful alternative to chalk.

We drew the same picture three times, one with each type of chalk, and tested how much water and how long each took to wear off.

Test #1

The first product tested was ordinary sidewalk chalk. An entire stick of chalk was used, and the center was filled in as completely as possible.

With a regular hose (no added pressure to the nozzle), the drawing was completely erased in seconds.

Test #2

Next came the soft pastels, which were purchased at a local arts shop. This drawing took nearly three pastels to draw, as they are much smaller than standard pieces of chalk. According to a worker at Blick’s Art store in Pasadena, this is the same drawing instrument used in the Pasadena Chalk Walk every year.

After a quick rinse with a limp hose, the drawing was somewhat erased, though there were noticeable marks left over that could not be erased with regular water pressure. With higher water pressure for a couple of minutes, the pastel came all the way off.

Test #3

The last product used was oil-based pastels. Nearly four pastels were used here, as they dissolved quickly. As with all the other tests, regular water with no added pressure was used first on the drawing. The result: none of the drawing was removed.

With added water pressure (including holding the hose at a close proximity to piece of art) and scrubbing the picture, it took nearly 20 minutes for the drawing to be erased. Even then, there were still faint traces of the colors left over.

So, depending on the drawing tool used, clean up could be radically different. Sidewalk chalk only needs a limp hose, whereas oil-based chalk could indeed require power-washing.

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