A generally accepted level of alkaline buffer added to paper intended for archival use is three to five percent. There are exceptions to the inclusion of alkaline additives, particularly with regard to papers meant for the preservation of certain protein based textiles and photographic materials, but we will address this issue later. Typically the alkaline buffer used in paper is calcium carbonate (CaCO3). Remember, an acid is any substance which can donate a proton, and we have seen the havoc a proton can inflict upon the bonds holding our paper together. A base, such as calcium carbonate, is any substance that accepts protons. The negatively charged (basic) hydroxyl unit (OH) combines with the positively charged (acidic) hydrogen ion (H) to form water. Assuming enough alkaline buffer (calcium carbonate) is available, the potential exists for the acid to be neutralized before it can damage the paper. This is why it is important to have alkaline buffering in all paper products used in conservation except, as mentioned earlier, those intended for use with certain protein-based textiles and photographic materials where excess alkalinity could potentially cause problems.