NGC Collection Management & Storage 2 — Questions and Answers
Question 1: Which environmental condition poses the greatest long-term risk to silver coins stored in a home collection?
- Low humidity below 30%
- Hydrogen sulfide gas from rubber or wool (Correct answer)
- Ultraviolet light from fluorescent bulbs
- Carbon dioxide from normal air
Correct answer: Hydrogen sulfide gas from rubber or wool
Hydrogen sulfide gas, emitted by rubber bands, wool, and certain plastics, reacts with silver to form silver sulfide toning and tarnish.
Question 2: What does the term 'PVC damage' refer to in numismatic coin storage?
- Physical abrasion from rigid plastic flips
- Green slime residue from plasticizers in soft vinyl holders (Correct answer)
- Discoloration caused by polyvinyl chloride powder
- Scratching from PVC-coated coin albums
Correct answer: Green slime residue from plasticizers in soft vinyl holders
PVC (polyvinyl chloride) flips contain plasticizers that leach out over time, leaving a green, oily residue on coin surfaces that can etch the metal.
Question 3: When building a type set of U.S. coinage, what organizational principle is typically followed?
- Collecting one coin of each design type regardless of denomination (Correct answer)
- Assembling complete date-and-mint runs for every series
- Acquiring the highest-grade example of every year minted
- Focusing only on coins struck before 1900
Correct answer: Collecting one coin of each design type regardless of denomination
A type set consists of one representative coin for each major design type, emphasizing design variety over complete date-and-mint runs.
Question 4: Which of the following is the safest long-term storage medium for paper currency and banknotes?
- Kraft paper envelopes
- Archival polyester (Mylar) currency sleeves (Correct answer)
- Standard polypropylene zip-lock bags
- Cellophane display sleeves
Correct answer: Archival polyester (Mylar) currency sleeves
Archival-grade polyester (Mylar/Melinex) sleeves are chemically inert, acid-free, and non-reactive, making them ideal for long-term banknote preservation.
Question 5: A collector discovers that an old 2x2 cardboard flip has left a ring impression on a coin's surface. What caused this?
- Acid migration from the cardboard staple area (Correct answer)
- Moisture trapped between the coin and cardboard
- Ink transfer from printed text on the flip
- Static electricity attracting dust particles
Correct answer: Acid migration from the cardboard staple area
Acids in non-archival cardboard can migrate to the coin's surface, leaving a ghost ring or stain corresponding to the flip's window or edge.
Question 6: What is the recommended relative humidity range for long-term coin storage?
- 20–30%
- 35–55% (Correct answer)
- 60–70%
- 75–85%
Correct answer: 35–55%
A relative humidity of 35–55% prevents both desiccation cracking (too dry) and oxidation or mold growth (too humid) on coin surfaces.
Question 7: Which practice best protects a coin collection during a home move or transport to a show?
- Wrapping individual coins in aluminum foil
- Placing slabbed coins loosely in a cardboard box
- Using padded, lockable cases with foam inserts rated for coins (Correct answer)
- Carrying coins in cloth coin purses to absorb shock
Correct answer: Using padded, lockable cases with foam inserts rated for coins
Padded, lockable cases with coin-safe foam inserts prevent mechanical shock, abrasion, and unauthorized access during transport.
NGC Collection Management & Storage 2
Which environmental condition poses the greatest long-term risk to silver coins stored in a home collection?