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Lead Pencils: Do they contain Lead (Pb)?

 Anand S. Burange
Department of Chemistry, Wilson College, Mumbai, India


 Motivation for writing this blog is an occurrence of one incident few months back in our Wilson College. In Mumbai University syllabus for second year undergraduates, we have chromatographic separation (paper chromatography) of metal ions where mixture of metal salts is spotted on paper and further run in mobile phase (acetone:HCl). Since different metal ions have different retention factors; they can be easily separated and then identified by using complexing agents to form coloured complexes on a paper. During the practical, when students were asked by my colleague Thomson (Asst. Professor) to put one spot and draw a line on a paper by pencil (to calculate Rf values later), one student raised query that lead pencil contains Pb (metal), and it should also show spot alike other metal. At that time, many students believed that lead pencil contains lead (Pb) and I also got same experience with my practical batch.

From childhood, right from nursery education to schooling and college studies we use lead pencils. We all are well aware about toxic effects and health hazard of Pb (Lead) on human beings. Lead exposure in children shows severe neurological effects which may lead to ataxia, coma and even death. Many children, I have often observed keeping pencils in their mouth. If Pb is so dangerous then why it is used in pencils?
The answer to above question is NO. In lead pencils, there is no Pb (Lead) present and it is safe to use. Then why do we call it lead pencil if there is no Lead (Pb)? Metallic lead (Pb) has no relation with lead pencils. The confusion is because of the fact that graphite is also known as plumbago and for long time people thought that it contains lead. The word plumabago derived from word "plumbum" which means lead (Latin).

 The most basic raw materials used for lead pencils are
 a) graphite 
 b) clay  and 
 c) wood
From a pencil expert, N.N. Godbole in 1945, " A lump of graphite from Ceylon, a handful of clay from Austria, a few sticks of soft red cedar from Florida, properly worked together by pencil machinery and skilled labour, produce the lead pencil of common use."

The graphite which is present in nature is suitable for pencils rather than synthetic graphite (Acheson graphite). Synthetic graphite is not appropriate for pencil manufacture may because of its physical structure.
For the first time graphite or plumbago was used in the reign of Queen Elizabeth where the first mine of graphite was discovered in Borrowdale, Cumberland in England in 1564. In her (Queen) time, graphite from said mine was so pure, it was used as it is and it could be cut into convenient chunks for the further use. Soon supply of graphite was exhausted and A. W. Faber from Germany came into picture. He set up huge industry and had great monopoly in pencil business in those time. Faber used some sort of sticky material to hold graphite particles. Later on many countries, especially America entered into pencil business. 

List of few famous old graphite mines during Pencil industry revolution

Eureka Black lead mine at Sonora in California
Borrowdale mines in Cumberland
Travancore, Tinnevelly and Godaveri , etc. districts in India 
 Ceylon
Among all, Ceylon graphite is world’s best because of its purity which contains 98.55% Carbon. In nutshell, there is no Pb in lead pencils. While reading details about pencil industry, I came across a book “Manufacture of Lead and Slate Pencils” by Dr. N. N. Godbole (Ph.D. Berlin), Edition year 1945. I recommend this book for the readers those who are interested to know details about Pencil manufacturing. In this book you can find history of pencil industry, Indian contribution, method of manufacturing, machineries used, how coloured pencils are made?, slate pencils manufacture, Pencil factories in India, etc.

 Hope this blog will aware the undergraduate students about the materials which they are using from long time as a lead in pencils. 


Comments

  1. Disha Biswas30 September 2020 at 05:52

    Very informative Sir. I will for sure read that book. And this was quite eye opening as even I thought it contained Pb.

    -FY student ( DIV C )

    ReplyDelete
  2. Komalika ninawe30 September 2020 at 06:59

    Sir lead pencils are made form lead, a form of graphite, but graphite are also minimally toxic as it is an allotropy of carbon, not that harmful but still it have a little danger for children.
    Thanks sir,It was very informative sir.

    ReplyDelete
  3. Dev Rajde3 October 2020 at 23:38

    Very Much Informative Sir
    And Interesting Too ,
    You Have Changed My Perspective
    In Terms Of Chemistry

    ReplyDelete
  4. NOOR AFSHA SODAWALA6 October 2020 at 20:59

    Sir it's really really informative enjoyed a lot thank u

    ReplyDelete

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