Peat Cardstock. 
The modern world runs on paper. Most paper comes from wood pulp, that is, trees. Peat also comes from trees, but has been allowed to ferment in water for thousands of years. Thus, Ireland should have no problem with paper. But that isn’t so. Yes, Peat was created from trees – oak trees – which are high in tannic acid and other organic acids which gives it the taste, and when burned, the aromatic smell. Paper can be made from peat, but with the high acid content, it doesn’t last long, especially in damp climates. The dark color also stains the resultant paper. While these problem areas can be overcome by additional processing, it increases the cost significantly to make peat paper uneconomical.
All this being said, peat has a special place in the Irish environment, in fact, has become synonymous with Ireland although it occurs in many other locations. Thus, small amounts of cardstock have been made to create covers, such as the REM envelope (Figure 1) from the mid-1920’s when foreign exchange money was tight, and use of local items was given preference. It has also been used at various times to creaate uniquely Irish postcards. Should you find an item made from peat cardstock, use a de-acidifier, such as Archival Mist ™, to neutralize the acid, and protect it from moisture be sealing it in an airtight plastic bag with a silica gel drying capsule.