Marble Moulds

These amazing Infinite Rim marble moulds were designed by American glass artist Drew Fritts.  His story is told below:

The Design

The Infinite Rim mould is a new style of graphite mould that has tapered holes, rather then the traditional hemispherical cups.  I came up with this design after analyzing the way that I was using traditional cup-style moulds – using the rim of the hole for rounding, rather than the cup.  The problem with using the rim of a traditional cup-style mould is that many times the cup sizes available are just not right for the marble being made.  This usually causes one of two situations:  either the marble goes down into the cup too far and the glass binds or catches on the rim, or too little of the marble fits into the cup, resulting in inefficient or negligible rounding.

In the past, some marble makers have solved these problems by having graduated sets of graphite ring moulds made.  Although the desired result of having the right size “rim” for any size marble is achieved with this method, the rings themselves are fairly fragile, and a full set is extremely expensive.  I decided there had to be another solution.

My first thought was that a single tapered hole would allow me to round any marble as if it were riding on the rim of a traditional cup-style mould.  Theoretically, a tapered hole provides an infinite number of “rims” because a sphere will contact the inner surface of a cone in a circle [Figure 1].  Therefore, no matter how much glass is in the gather, spinning it in a conical mould should make it round!  Unfortunately, there is a major design flaw in trying to use just one tapered hole for all sizes of marbles – namely, the marble can’t be rotated horizontally if it’s too small.  This is because when the marble goes too far down into the hole, the punty hits the rim of the mould!  [Figure 2]


figure-1.jpg figure-2.jpg
Figure 1 Figure 2


The design I ended up with is a series of overlapping, round bottomed cones, providing an infinite possibility of “rim” sizes that currently span from approximately 3/8″ to over 6″  (Custom moulds can be developed.)  Each Infinite Rim mould is designed to round any marble within a given size range.  I mathematically designed the hole angles so that any marble that fits into the hole will be rounded as if it were being rounded on the optimal size cup rim or ring mould, therefore avoiding all of the problems that arise when rounding marbles.  And best of all, because of the design, these are absolutely the easiest graphite moulds to use!  The marble practically rounds itself!


I LOVE this mould!  It’s the best darn mould ever!

– Josh Sable

Referring to a prototype 2″ Infinite Rim mould



When I decided I wanted to have these moulds produced I approached Dan Grumbling with the design.  Dan had made some of my traditional cup-style moulds, and in my opinion they were some of the best quality moulds on the market.  Dan uses only the best quality graphite, has excellent craftsmanship, and his attention to detail is superb.  Well… Dan and I spent the next 5 months designing and prototyping all of the rest of the details of the moulds to make sure that we had the best moulds possible for the money.

  1. The moulds are made from EDM graphite – the best, slickest, smoothest graphite available.
  2. The graphite is attached to the handle using the same type of band-clamp mounting system that Dan had been using on his traditional moulds.  This system has several advantages.
    • The handles are custom-turned titanium which provides a lightweight, durable handle that won’t burn, warp, or conduct heat. And the attachment method provides for a non-slip, twist-proof attachment.  The handle will never slip or twist – guaranteed!
    • Minor wear and tear is easily maintained:  For example, if your punty always contacts the rim in the same place because of the angle you hold the mould, it may wear an indentation in the rim over time.  If this occurs simply loosen the band, spin the mould to a new position, and retighten the band.
    • If the graphite mould gets broken in a fall, or severely damaged for any reason, it can easily be replaced by loosening the band, removing the graphite puck, slipping in a new puck, and retightening the band.  This saves on some of the cost of buying a completely new mould in the unfortunate event that it’s necessary.
  3. Each handle is 10″ long overall to accommodate different working styles.  Some people like to choke up close to the mould, while others like to hold further back on the handle to keep their hand away from the heat.
  4. The handle is counterweighted with a custom-fitted, swirled, pewter-like knob on the end.  On the smaller moulds this places the balance point very close to the center of the overall length and makes the mould very easy to maneuver.


  5. NOTE:Moulds can be order without handles. Custom mounting brackets designed to hold the mould on the work surface can also be ordered. This is especially important with the larger sizes.


There are currently eight moulds available covering the range 3/8″ to 6″ diameter.  The smaller sizes are contained in a multi-hole mould, and the larger sizes are in individual moulds.

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