Letters to the editor

Re: Cobalt complex ions: Le Châtelier's Principle, May 2017 and
Borax advisory update Health Canada, April 2017

Davis's excellent article (Cobalt complex ions…) reminded me of a demonstration I did to "pretty up" my classroom in the mid '70s. I was attempting to imitate the reaction of cobalt(II) chloride paper — after over 40 years I cannot recall where I found this demo. An Erlenmeyer-shaped flask was cut out of some absorbent paper and soaked in a solution of cobalt(II) chloride. When the paper had dried the now blue flask was attached to the classroom wall.

In the course of everyday teaching the flask rarely (if ever) got noticed. One day, years later, a student remarked "Sir, yesterday the flask was blue and today it is pink". Bingo, a teachable moment! Warning: the demo will not work well in schools that are climate controlled.

I read the article “Borax Advisory Update Health Canada” with a bit of trepidation. My initial instinct was “Here we go again! Chemophobia raises its ugly head.” Schools using proper safety procedures should have no issues with making slime the traditional way. The greater challenge is informing the general public, because a number of readily available borax/boric acid containing products may be found in the home. Lab safety procedures frequently do not transfer to the home setting.

The second article “Starch in Place of Borax” gives the impression that using the Sta-Flo laundry starch eliminates the contact with borax. Sta-Flo starch actually contains borax, which is indicated in its MSDS (SDS). Other liquid starches may or may not contain borax. Linit, another popular brand in the US, also contains borax. Summarizing my past experiences, if a starch product contains borax, slime is produced. If the product has no borax, no crosslinking occurs, ergo, no slime. Utilizing the laundry starches reduces the amount of borax in making slime, but does not eliminate it. I have not used the Niagara spray starches. Both the aerosol and non-aerosol spray contain ethylene glycol. There is no mention of borax in any of the MSDSs. The aerosol spray contains a flammable mixture of propane, butane and isobutene as the propellant.

Ed Escudero (retired)

Summit Country Day School, Cincinnati OH

Re: Borax advisory update Health Canada, April 2017

In the 1970s, my colleagues and I made Elmer’s Glue® putty using liquid starch. Then, there came a time that the recipe we were using did not work. Inquiries to the manufacturer of the starch revealed that the liquid starch contained borax (sodium tetraborate) and the company had removed it from their formulation. We then used a solution of borax to make the Elmer’s Glue® putty.

In 1978, when I spoke with a representative from Mattel Toy Company, I learned that Slime® was made from guar gum crossed-linked using borax. After working out a recipe, I shared that recipe at conferences including ChemEd 79. The recipe for PVA Slime was developed by the late David Weil and shared at ChemEd 81.

In the April 2017 issue, Dave Gervais’s borax advisory article stated that “glue- and borax-free recipes are available…” Included with that article was “Starch in place of borax” by Ken Lyle and Kacey Hall.  Unfortunately, this option does not solve the borax problem. According to its SDS1 the Sta-Flo® Liquid Starch does contain sodium tetraborate. To the best of my knowledge, Niagara® Spray Starch may also contain borax, but their SDS2 does not list ingredients and states “The specific chemical identity and/or exact percentage of composition have been withheld as a trade secret [29 CFR 1910.1200]”. The recommendation of substituting liquid or spray starch does not eliminate borax from the recipe and now includes a number of other substances including tetrasodium EDTA, sodium hydroxide and sodium metabisulfite. An additional problem would occur if the recipe using starch does not work; then the experimenter would probably add additional amounts of the starch increasing the amounts of other substances. Recipes, found online, using liquid laundry detergent do not remove borax as it is a common builder in detergents, and, again, adds a number of other ingredients to the final product.3

It is my opinion that a solution of borax can be safely used in making slime-type materials, that the proper safety instructions be given to the teachers and experimenters and the precautions as listed in Dave Gervais’ article should be observed. Under no circumstances, however, should powdered borax be used directly in any preparation of slime-type materials.

David A. Katz, Chemist and Educator, Tucson, AZ www.chymist.com


  1. https://householdproducts.nlm.nih.gov/cgi-bin/household/brands?tbl=brands&id=4002416
  2. https://info.faultless.com/msds/ns/Niagara%20Spray%20Starch%20(aerosol).PDF
  3. Compound lists in two popular laundry detergents, Tide & Persil, Chemical & Engineering News, January 23, 2017