To Slab or Not to Slab Ancient Coins?

August 29, 2024

By Mike Markowitz for CoinWeek …..

A persistent controversy among ancient coin collectors is the question of encapsulation or “slabbing”. Many older collectors regard slabs as “plastic coin prisons” that spoil the appreciation of ancient artifacts. These collectors want to experience the thrill of touching something ancient Greeks and Romans handled.

On the other hand, many younger collectors are reassured knowing that an expert has examined and graded the coin (although this does not necessarily guarantee authenticity). They like the security of having the coin sealed in “archival” materials for long-term storage and the convenience of carrying it around in a pocket.

Classic collectible American coins are mostly slabbed these days and trade at prices largely determined by their rarity and grade, but this is less true for ancient and world coins. I have about a half-dozen slabbed coins out of almost 300 ancient gold coins in my collection. These are pieces that I purchased because the price was right and the type was rare or attractive.

In times past, collectors of ancient coins (generally wealthy aristocrats) stored them in custom-built cabinets. These were often superbly crafted masterpieces of carpentry, valued today as antiques. Coin trays in such cabinets were usually lined with soft felt or velvet, which gives us a term used in technical numismatic grading: “cabinet friction” – the slight polish or wear on coin surfaces caused by rubbing against this fabric lining.

As ancient coin collecting became more of a middle-class hobby in the 19th century (favored by doctors, lawyers, and clergy–the “learned professions” that had studied Latin and Greek), coins were increasingly stored in paper envelopes and gathered in cardboard boxes. This was problematic since old paper and cardboard were processed with sulfuric acid, which can leave chemical residues harmful to many coin surfaces – especially under humid conditions. Old paper made from wood pulp also becomes brittle over time.^[1] Acid-free paper^[2] suitable for archival storage was developed only in the 1950s.

Today, most ancient coins are sold in “flips”, plastic sleeves about two-and-a-half inches square that contain two pockets – one for the coin, the other for a paper or card label. Soft, flexible flips made of PVC (polyvinyl chloride^[3]) are NOT safe for long-term coin storage: they contain “plasticizers” that can leave a harmful and unsightly residue on coins. “Safety flips”^[4] made of polyethylene terephthalate^[5] are stiff and somewhat brittle but considered an inert archival material.

An inexpensive form of coin encapsulation that became popular in the 1960s was a square cardboard holder with round cellophane-covered windows for both sides of the coin. These are either stapled shut or secured with an adhesive.

1921 Italian 10 Ct. in 2"x2" flip. Image: Mike Markowitz. — 1921 Italian 10 Ct. in 2″x2″ flip. Image: Mike Markowitz.

ANACS, founded by the American Numismatic Association (ANA) in 1972 as a grading service, began encapsulating coins in plastic holders in July 1988. PCGS (Professional Coin Grading Service) entered this market in 1986. Neither of these firms grades and encapsulates ancient coins. Founded in 1987, NGC (Numismatic Guaranty Company) began offering grading and encapsulation of ancients in 2009 under the supervision of numismatist David Vagi, author of the two-volume Coinage and History of the Roman Empire (1999).

An innovation of the NGC program is the “EdgeView” holder, which allows most of the coin’s edge to be viewed obliquely. The coin is held in place by four soft plastic prongs. This can be important to collectors since a visible casting seam along the edge is often diagnostic of a fake.

NGC-certified AV solidus of Justinian II. Image: Mike Markowitz / CoinWeek.

Every coin gets a serial number, a bar code, and (recently) a QR code that links to an online database, allowing it to be easily referenced.

NGC-certified AV tremissis of Constans II. Image: Mike Markowitz / CoinWeek.

NGC uses a five-point grading scale, with 5 being the highest grade. NGC evaluates the coin on two separate dimensions – “strike” and “surface”:

The primary considerations for Strike are centering, strength of strike, evenness of strike, striking cracks, planchet imperfections and die state.

The primary considerations for Surface quality are luster, corrosion, porosity, encrustation, silvering, cleaning, marks, hairlines and scratches.

Since the dies used to strike ancient coin dies were hand-engraved, style can vary greatly from one die to another, even among coins from the same series. The Style of each coin will be carefully evaluated, and any coin of superior style will be awarded the designation “Fine Style”.^[6]

The cost of encapsulation is a complex subject. There are a wide variety of options, and pricing depends on the assessed market value of the coin.^[7] The basic “Economy” level service for coins valued at $300 or less was $33 per coin at the time of this writing, plus shipping and handling. Express service costs more.

Heritage Auctions^[8], a major player in the ancient coin trade, has almost all the coins in its auctions graded and encapsulated by NGC.

For collectors who do not require grading, there is a wide variety of do-it-yourself encapsulation options. An early form of “proto-slab” was sold by Capital Plastics^[9] many years ago.

Gold solidus of Constantine in Capital Plastics holder. Image: Mike Markowitz / CoinWeek.

Three sheets of plexiglass were sandwiched together and secured by plastic or metal screws at the corners. The middle sheet had a round cutout to fit the coin, with space for a label. Removal of the coin is relatively simple. Today, Capital Plastics sells a range of capsules in different sizes intended for collectible American coins.^[10]

I was given some plastic coin holders a while ago that were original mint packaging for foreign silver coins. I recycled them to hold a few of my coins for a classroom demonstration.

Discarded holder repurposed for a classroom demonstration. Image: Mike Markowitz.

The pocket for the coin was much too large, and the coins rattled around a bit. But they were securely encapsulated, and this solution worked well to pass around.

The German firm Leuchtturm (“Lighthouse” in English) produces a line of “Quickslab”^[11] products in the exact size of NGC slabs (3 3/8” x 2 3/8” x 3/8″ or 85 x 60 x 10 mm), so they will fit standard slab storage boxes.

Leuchtturm Quickslab. Image: Mike Markowitz.

A soft foam insert is sandwiched between upper and lower clear shells that snap together securely. A tool can be inserted into a small slot to snap the shells apart. The foam is made from the archival material EVA (ethylene vinyl acetate^[12]). The cutout that fits the coin is available in sizes from 14 to 41 mm. For smaller coins, there is often enough room above the cutout to insert the 2” x 2” label from a flip.

Electrum stater of Carthage in Leuchtturm Quickslab. Image: Mike Markowitz / CoinWeek.

Original dealer labels or collector tags help to document a coin’s provenance and should be carefully preserved whenever possible.

Removal of a coin from its sealed encapsulation involves the careful mechanical destruction of the slab to avoid damaging the coin. Some collectors refer to this process as “jailbreaking”.

Ancient coin cracked out of an NGC holder. Image: Mike Markowitz.

This is sometimes done to re-submit a coin to get a better grade. A search on YouTube for the phrase “cracking out a coin slab” or similar will bring up numerous video clips demonstrating how this can be done.

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