Sunday, October 2, 2016

What is archival watercolor paper?

There are many terms associated with paper, all useful for the artist to know. Here I make an attempt to sort a few of them out.

Acid free paper / Syrafritt papper

  • Paper with a neutral or basic pH value (7 or slightly greater)
  • Can be made from any cellulose fiber (plant based) as long as the acid in the wood pulp is removed/neutralized
  • Sizing additives must also be acid free
  • Lignin and sulfur free  
  • Much more durable than acidic wood-based paper

Lignin/ Lignin

  • Lignin is a substance in the cells and cell walls of wood and most plants, making them rigid

Sulfur / Svavel

  • Sulfur is a chemical element that is used in several chemical methods producing wood pulp from wood

Wood-based paper/ Trä-baserat papper, cellulosapapper

  • Made from wood pulp
  • Contains acids, acidic
  • Contains lignin
  • Turns yellow and brittle with time
  • Deteriorates faster if exposed to light and/or heat

100% cotton paper / 100% bomull eller lump


  • Made from 100% cotton linters or cotton from used cloth (rag, also called rag paper)
  • May still contain some acids so should be tested/certified before use as archival paper
  • Stronger and more durable than wood based paper

Permanent paper, ISO 9706 / Åldringsbeständigt papper (ISO 9706)

ISO stands for International Organization for Standardization.
  • pH value between 7.5-10.0 / pH-värde
  • Alkali reserve of at least 0.4 mol acid per kg paper (at least 2%) (neutralizes acid from aging or pollution) / Alkalisk reserv
  • Tearing resistance of at least 350 mN (index of durability) / Rivstyrka
  • Kappa number of less than 5.0 (may contain only a small amount of easily oxidized material, about 1% lignin) / Kappatal
  • This standard does not cover optical properties, such as brightness

Archival paper, ISO 11108 / Arkivbeständigt papper eller arkivpapper (ISO 11108)

  • Made from cotton, cotton linters, hemp, flax, or mixtures thereof, but may contain a small amount of fully bleached chemical pulp
  • Folding endurance of at least 2.18 (MIT, Köhler Molin, or Lhomargy instrument) or 2.42 (Schopper instrument) / Vikstyrka
  • Archival papers also meet the requirements for permanent paper

Permanent paper, ANSI/NISO Z39.48-1992 (R2009)

ANSI/NISO stands for American National Standards Institute/National Information Standards Organization. ANSI/NISO Z39.48-1992 (R2002) is an American standard similar to ISO 9706 for uncoated and coated paper.

Uncoated paper
  • pH value in the range of 7.5-10.0
  • Minimum alkaline reserve equivalent to 2% calcium carbonate
  • Tear resistance of at least 5.25 mNm2/g
  • Kappa number no greater than 7 (shall contain no more than 1% lignin) 

Coated paper

  • pH value of core paper in the range of 7.0-10.0 . The paper as a whole (core and coating) must meet the alkaline reserve requirement
  • Minimum alkaline reserve equivalent to 2% calcium carbonate
  • Tear resistance of at least 3.50 mNm2/g (this generally equals a core tear resistance of 5.25 mNm2/g)
  • Kappa number no greater than 7 (may contain no more than 1% lignin) 

Conclusion

There are several ways to define archival paper, both in terminology and different types of certifications.

Even the definitions themselves may vary between standards, for example, also a slightly acidic paper may in some instances be considered acid-free!

And, as long as the paper follows the requirements, long-term effects of for example additives may yet to be discovered!

Still, when I look for a long-lasting paper, I look for a 100% cotton, acid-free paper, keeping in mind that other factors also affect the longevity of the paper.

Environmental factors such as heat, light, humidity, acidity all have an effect on paper, as do the ways paper is stored (do not store between acidic sheets of paper or on wood, for example) and handled (best handled with cotton gloves), as well as the pH of the water you are using to paint.


References

Översättning. En kort ordlista relaterad till beständighet hos akvarellpapper, inkl. syrafritt papper, träbaserat eller cellulosapapper, papper av 100% bomull samt ett par olika certifieringar (ISO 9706 och ISO 11108).

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