I constantly have exams that require to shade bubbles on an optical answer sheet. Usually I will shade it with a 0.5 (2B) lead mechanical pencil. I think I shade quite hard sometimes(not sure if the pressure matters), then when I try to erase my choices on the bubble, I realise there are still some remains on it (about 50% of its previous darkness) on the bubble, and I do not know if the machine will still detect that previous bubble as filled and be unable to conclude my final option.

Is there a way to get a good way to do exams related to these? Like getting a good eraser from a certain brand or making sure my eraser can lead to a cleaner erasing job?

3 Answers 3


A technique that I use that may help. I use a two-step approach.

No problem with the questions I know. I answer them and move on.

I answer the questions with a small, light "x" mark in the answer bubble if I have any question about the answer being the correct one. It's dark enough for me to see it easily.

Near the end of the exam, I review the lightly-marked answers and darken them in after I'm sure of my response.

This GREATLY REDUCES the need to use much time and effort to change a questionable answer.


Pencils have a lead core made with different proportions of two materials to make different kinds of marks on a material.

One material is clay to hold the shape of the marking pigment and the second is graphite which is the black pigment that makes the visible mark.

An HB pencil is half clay and half graphite. The "H" represents the "Hard, stiff clay" and the "B" represents the "black graphite."

Pencils come in a range from hardest to softest starting with 5H, then progressively 4H, 3H, 2H, HB, 2B, 3B, 4B, 5B getting progressively darker with more graphite (very soft stuff). Some expensive sets have a range from 7H to 7B. They can be bought independently and you can also buy leads in grades to fit lead holders and mechanical pencils. Avoid putting soft leads in cheap mechanical "clutch" pencils as they will crumble in the pencil works.

You want to avoid hard pencils that will scratch the paper and need more pressure than a softer, darker one.

You must also not press too hard with a soft pencil or you will have too much graphite which will smudge and be difficult to clean up if you make an error.

A hard eraser will damage the paper. A soft white plastic one will be kinder to the paper but needs to be clean to work. The soft lead will dirty the eraser so that you must be sure to only use the clean part of the eraser to avoid smudging.

Using an eraser effectively is another issue. Start to one-side of the part to be erased instead of putting it into the middle of the error. Work from a clean area into the dirty part gradually removing the mistake as you work across it. Be sure your eraser is clean or it won't remove the graphite mark.

The thickness of the pencil is less of an issue than the hardness. A 0.5 is only 0.2mm thinner than the 0.7 so the mark will be thinner and require less effort to make the same dark line. The force is concentrated into a smaller area of the tip which increases the pressure. Some prefer a wide stroke and some a narrow one. That's a personal preference.

White plastic erasers work best with dark leads. Some (with colours and grey) have fibres embedded in them to abrade (scratch) the surface to better remove ink and other more permanent pigments that sit on the surface of coated (they look shiny or have a slight gloss) paper. stocks.

Short answer: Use a soft lead so you don't need much pressure and a white eraser to remove mistakes.

  • Can you clarify what u meant by "Avoid putting soft leads in cheap mechanical "clutch" pencils as they will crumble in the pencil works." I dont know if my mechanical pencil is the problem or the lead is the problem. I use a 0.5 2B pencil lead, and maybe I have the habit to shade very hard ... Oct 2, 2018 at 14:50
  • @PrashinJeevaganth Don't go to an art store and buy a 10-lead package of 7B leads to go into a cheap mechanical lead holder. They will crumble inside the holder if the lead holder is not a high-quality one. The art store will be able to guide you but you may be surprised because of the high cost of what you may think you will be able to get elsewhere cheaper. The quality of the holder is not immediately apparent by appearance alone.
    – Stan
    Oct 2, 2018 at 15:00
  • @PrashinJeevaganth You are comfortably in the middle zone with all aspects of your question. The things you mention sound perfect. The problem might be with how hard you press. Stress of exams might cause you to be more tense and express it when you answer your exam questions.
    – Stan
    Oct 2, 2018 at 15:17
  • Will sweat cause difficulty in erasing too? I'm been on a higher dosage of caffeine recently and started developing sweaty palms. When you meant the mechanical lead holder, do you mean the tube containing the lead? If so, my leads are all still intact for as long as I use it. Oct 2, 2018 at 15:20
  • @PrashinJeevaganth Rest your hand on another piece of paper so your sweat cannot moisten the surface of the answer sheet. Yes, I mean the tube holding the pencil lead. It's usually made of plastic and metal. Good luck in your endeavours.
    – Stan
    Oct 2, 2018 at 15:29

Try ticker (0.7) and softer lead (2B), and the blue part of the eraser. Don't apply too much pressure when using the pencil and try not to perforate the paper with the eraser. eraser

  • My lead is already 2B, but why is 0.7 better than 0.5? I thought the finer pencil lead should be easier to erase? Also, I would have to look for such an unique eraser with 2 different sides, I usually use the conventional full white ones. Oct 2, 2018 at 11:15
  • The blue part of these erasers is for ink or similar pens and contains abrasive particles. It will remove some of the paper or at least scratch the surface. It needs practice to use it correctly and effectively. Depending on the type of exam paper, using it in an exam may be a really bad idea.
    – Stephie
    Nov 6, 2018 at 21:27

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.