Chalko, Chalkboard Liquid Markers, set of 4 markers.  These are really fun to use and easy.  They work great, and the write very smooth.  I have not issues with clumping, or uneven writting. Simply shake and push in the tip, shake again, push in tip and the liquid will flow into the tip and your ready to go.  I was wrote on my fish tank, bathroom mirror and of course a chalkboard.  These are not like old school chalk.  Very pleased with how smoothly the liquid chalk came out.  If your needing a great working chalk this is the one to get.   Thank you for allowing me to try your product  I recommend this product. Disclosure: I received this product at a discount in exchange for my honest  and unbiased review.  I have no affiliation with this company.

http://www.amazon.com/gp/product/B017581PYY?keywords=chalk%20markers&m=A3VQE9PFZG2FR2&qid=1456993997&ref_=sr_1_1&s=merchant-items&sr=1-1

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