question: What allows an eraser to remove just either pencil trace or ink from paper and how?
comment: Pencil lead and certain inks will sit upon the paper, rather than soaking into the paper. An eraser is literally just rubbing it off. You can achieve a similar effect using your finger, but the oil in your fingers were generally mix with the graphite and you'll just kind of smear stuff. Rubber is dry and has no oils in the outer layers of the eraser won't rub off as well, exposing fresh rubber.
passages: Most pencil cores are made of graphite powder mixed with a clay binder. Graphite pencils (traditionally known as 'lead pencils') produce grey or black marks that are easily erased, but otherwise resistant to moisture, most chemicals, ultraviolet radiation and natural aging. Other types of pencil cores, such as those of charcoal, are mainly used for drawing and sketching. Coloured pencils are sometimes used by teachers or editors to correct submitted texts, but are typically regarded as art supplies—especially those with waxy core binders that tend to smear when erasers are applied to them. Grease pencils have a softer, crayon-like waxy core that can leave marks on smooth surfaces such as glass or porcelain.
   Tombow
  
  Section::::Products.
  
  Tombow's range of products include:
  
  Section::::Products.:Mono.
  
  Mono is one of Tombow's most popular product lines. It comprises different types of pencils, erasers, and correction tapes. Some product examples include the Mono plastic eraser (see image), the Mono Graph pencil, and the Mono correction tape.
  
  Section::::Products.:Brush pens.
   A whiteboard marker, or a dry-erase marker in some locations, uses an erasable ink, made to be used on a slick (or matte-finished), non-porous writing surface, for temporary writing with overhead projectors, whiteboards, and the like. They are designed so that the user is able to easily erase the marks using either a damp cloth, tissue, handkerchief, baby wipe, or other easily cleaned or disposable items. Generally, people use fabrics to do so, but others use items like paper, clothing items, some even use their bare hands to wipe it clear. The erasable ink does not contain the toxic chemical compounds xylene and/or toluene as have been used in permanent markers, being less of a risk to being used as a recreational drug.
   Pencil
  
  A pencil is an implement for writing or drawing, constructed of a narrow, solid pigment core in a protective casing that prevents the core from being broken and/or marking the user's hand.
  
  Pencils create marks by physical abrasion, leaving a trail of solid core material that adheres to a sheet of paper or other surface. They are distinct from pens, which dispense liquid or gel ink onto the marked surface.
   BULLET::::- Erasable colour pencils: Unlike wax-based coloured pencils, these can be easily erased. Their main use is in sketching, where the objective is to create an outline using the same colour that other media (such as wax pencils, or watercolour paints) would fill or when the objective is to scan the colour sketch. Some animators prefer erasable colour pencils as opposed to graphite pencils because they don't smudge as easily, and the different colours allow for better separation of objects in the sketch. Copy-editors find them useful too, as their markings stand out more than graphite but can be erased.
   The chemical ink eradicator contains a substance that reacts with some inks removing their pigmentation and hiding the writing.
  
  Section::::Metal ink erasers.
  
  Metal ink erasers were generally used before chemical ink erasers were introduced, and when permanent writing was done in ink. The erasers were essentially small knives.
  
  Section::::Chemical ink erasers.
  
  The chemical ink eraser was invented by the German manufacturer Pelikan in the 1930s, and was introduced as a novelty in Germany in 1972 under the name "Tintentiger" (ink tiger).
   Erasers may be free-standing blocks ("block" and "wedge eraser"), or conical caps that can slip onto the end of a pencil ("cap eraser"). A "barrel" or "click eraser" is a device shaped like a pencil, but instead of being filled with pencil lead, its barrel contains a retractable cylinder of eraser material (most commonly soft vinyl). Many, but not all, wooden pencils are made with attached erasers. Novelty erasers made in shapes intended to be amusing are often made of hard vinyl, which tends to smear heavy markings when used as an eraser.
  
  Section::::Types.
  
  Section::::Types.:Pencil or cap erasers.
   Felt chalkboard erasers or blackboard dusters are used to erase chalk markings on a chalkboard. Chalk writing leaves light-coloured particles weakly adhering to a dark surface (e.g., white on black, or yellow on green); it can be rubbed off with a soft material, such as a rag. Erasers for chalkboards are made, with a block of plastic or wood, much larger than an eraser for pen or pencil, with a layer of felt on one side. The block is held in the hand and the felt rubbed against the writing, which it easily wipes off. Chalk dust is released, some of which sticks to the eraser until it is cleaned, usually by hitting it against a hard surface.
   Section::::Types.:Poster putty.
   Section::::Types.:Kneaded erasers.
   Ink eraser
  
  An ink eraser is an instrument used to remove ink from a writing surface, more difficult than removing pencil markings. Older types are a metal scraper, which scrapes the ink off the surface, and an eraser similar to a rubber pencil eraser, but with additional abrasives, such as sand, incorporated. Fibreglass erasers also work by abrasion. These erasers physically remove the ink from the paper. There is some unavoidable damage with most types of paper and ink, where the paper absorbs some ink, but not all.
   At first, erasers were made to erase mistakes made with a pencil; later, more abrasive ink erasers were introduced. The term is also used for things that remove marks from chalkboards and whiteboards.
  
  Section::::History.
   Ballpoint pens with erasable ink were pioneered by the Paper Mate pen company. The ink formulas of erasable ballpoints have properties similar to rubber cement, allowing the ink to be literally rubbed clean from the writing surface before drying and eventually becoming permanent. Erasable ink is much thicker than standard ballpoint inks, requiring pressurized cartridges to facilitate inkflow—meaning they can also write upside-down. Though these pens are equipped with erasers, any eraser will suffice.
   Normal pencils, chalk, and crayons all share the characteristic that they cannot "run out". The useful life of these implements is closely linked to their physical existence. However, specialized accessories such as pencil sharpeners may be required to reshape the working end of the pigment core or to remove the outer casing from around the tip.
  
  Section::::Assisted.
  
  These require the presence of an added pigment in order to write, and are useless when "empty".
  
  Section::::Assisted.:Pens.
  
  The pen is the most common form of writing implement. It has a hard tip which applies ink to a surface.
  
  Section::::Assisted.:Pens.:Capillary-action dip pens.
   Originally made from natural rubber, but now usually from cheaper SBR, this type contains mineral fillers and an abrasive such as pumice with a plasticizer such as vegetable oil. They are relatively hard (in order to remain attached to the pencil) and frequently coloured pink.
  
  Section::::Types.:Artist's gum eraser.
   A clutch pencil (or leadholder) tends to use thicker leads (2–5.6 mm) and generally holds only one piece of lead at a time. A typical clutch pencil is activated by pressing the eraser cap on the top, to open the jaws inside the tip and allow the lead to freely drop through from the barrel (or back into it when retracting). Because the lead falls out freely when the jaws are opened, its forward movement cannot be controlled except by external means. This can be easily done by keeping the tip of the pencil a few millimeters above a work surface or the palm of one's hand. Some clutch pencils do have mechanisms which incrementally advance the lead, such as the Alvin Tech-Matic leadholder, but these are not normally considered to be in the same category as most pencils with propelling mechanisms.
   Various types of eraser, depending upon the board and the type of ink used, are used to erase a whiteboard.
  
  Dedicated erasers that are supplied with some ballpens and permanent markers are intended only to erase the ink of the writing instrument they are made for; sometimes this is done by making the ink bond more strongly to the material of an eraser than the surface it was applied to.
  
  Section::::See also.
  
  BULLET::::- Ink eraser
  
  BULLET::::- Chalkboard eraser
  
  BULLET::::- Kneaded eraser
  
  Section::::References.
  
  Section::::References.:Bibliography.
  
  BULLET::::- Petroski, Henry (1989). "The Pencil: A History of Design and Circumstance"..
  
  Section::::External links.
   Most brands of "OLFA" marker wipe off easily with acetone free nail polish remover, the kind containing ethyl acetate, a relatively non-toxic organic solvent.
  
  Some markers are designed to be long lasting, for instance by having two inks, one specialized to resist solvents, and one specialized not to fade. These can be available in refillable form.
   There are also pencils which use mechanical methods to push lead through a hole at the end. These can be divided into two groups: propelling pencils use an internal mechanism to push the lead out from an internal compartment, while clutch pencils merely hold the lead in place (the lead is extended by releasing it and allowing some external force, usually gravity, to pull it out of the body). The erasers (sometimes replaced by a sharpener on pencils with larger lead sizes) are also removable (and thus replaceable), and usually cover a place to store replacement leads. Mechanical pencils are popular for their longevity and the fact that they may never need sharpening. Lead types are based on grade and size; with standard sizes being , , , , , , , , and (ISO 9175-1)—the size is available, but is not considered a standard ISO size.
   "Dry highlighters" (occasionally called "dry line highlighters") have an applicator that applies a thin strip of highlighter tape (physically similar to audio tape) instead of a felt tip. Unlike standard highlighters, they are easily erasable. They are different from "dry mark highlighters", which are sometimes advertised as being useful for highlighting books with thin pages.
  
  "Gel highlighters" contain a gel stick rather than a felt tip. The gel does not bleed through paper or become dried out in the pen as other highlighters' inks may.
   The whiteboard pen (also called a whiteboard marker or dry erasable marker) was invented by Jerry Woolf of Techform Laboratories and later patented by Pilot Pen in 1975. It is a non-permanent marker and uses an erasable ink that adheres to the writing surface without binding to or being absorbed by it. Applications range from temporary writing with acetate sheets (for use with overhead projectors) to whiteboards and similar glossy surfaces. The erasable ink does not contain the toxic chemical compounds xylene and/or toluene, unlike permanent markers.
  
  Section::::Surface materials.
  
  There are six types of materials commonly used for whiteboard surfaces:
   Section::::Types.
  
  Section::::Types.:Permanent marker.
  
  Permanent markers are porous pens that can write on surfaces such as glass, plastic, wood, metal, and stone. The marks made by such pens are however, not permanent on some plastics like Teflon, polypropylene etc., and can be erased easily. The ink is generally resistant to rubbing and water, and can last for many years. Depending on the surface and the marker used, however, the marks can often be removed with either vigorous scrubbing or chemicals such as acetone.
  
  Section::::Types.:Highlighters.
   Kneaded erasers can be shaped by hand for precision erasing, creating highlights, or performing detailing work. They are commonly used to remove light charcoal or graphite marks and in subtractive drawing techniques. However, they are ill-suited for completely erasing large areas, and may smear or stick if too warm. 
  
  Although kneaded erasers do not wear away like other erasers, they can become saturated and unable to absorb any more graphite or charcoal. In that case a kneaded eraser will actually leave marks on the paper instead of erasing them.
   Copying pencil
  
  A copying pencil, also indelible pencil or chemical pencil, is pencil whose lead contains a dye. The lead is fabricated by adding a dry water-soluble permanent dye to powdered graphite—used in standard graphite pencils—before binding the mixture with clay.
  
  Section::::History.
   In spite of the name, pencil leads do not contain the toxic chemical element lead, but are typically made with graphite and clay, or plastic polymers. Compared to standard pencils, mechanical pencils have a smaller range of marking types, though numerous variations exist. Most mechanical pencils can be refilled, but some inexpensive models are meant to be disposable and are discarded when empty.
  
  Section::::Lead variations.:Diameter.
  