I’ve been in the position to have used or witnessed the offering in sulphur free clay from three of the main players, Chavant, Eberhard Faber and Kolb. To give you a more detailed description of how these clays face-off against each other, here is a more in depth review.

Chavant V130

• Compared to earlier versions by Chavant this finishes very well, allowing for spot check highlighting without the use of film by experienced modelers. Lesser experienced modelers will still have to view the traditional way, with dinoc or highlighting film.
• Once applied, the clay firms up very quickly which is good for instant modeling but can be a disadvantage, especially when priming bucks with a substantial amount of clay. A heat source would be advisable to ensure all clay layers adhere to each other to prevent delamination.
• Does not blend very well without an external heat source.
• Still has adhesion problems although better than previous versions.
• Substantially less abrasive than previous versions but still requires frequent sharpening of tools. The main culprit from the previous version was the glass spheres that were used for the filler, once the clay was brought up to temperature it blended very well but any length of time in the oven, i.e. 2-3 days would see a glazing of the billet surface. This glazed surface would not blend into the rest of the billet, giving an appearance of small pieces of shale in the mix, resulting in the steels skidding off the surface rather than cutting.
• Color still remains patchy due to aging in the oven and oven temperature change. Regardless of how consistent the oven temperature is the color will darken with age due to the materials used.
• Detailed edges are hard to repair or change. (Adhesion problems)
• Edges tear in any profile dragging process unless clay is keep very warm. This amounts to addressing small drag sections at a time as the clay cools very quickly. I would recommend an additional heat source such as a heat gun to rewarm surfaces prior to putting in any profile.
• Still susceptible to cracking. This you can probably put down to a 50/50 problem, 50% being the buck building process and 50% down to the lack of elasticity in the clay. The buck has to be tight, that is, no voids in foam joints and I mean, no gaps whatsoever otherwise the clay will eventually crack in that area. The clay has to be packed on correctly, in even layers and not by building up walls and filling in between.
• Machines very well although feed has to be slowed down to prevent cutter bounce.
• Machine finish is not as good as the sulphur based clays.
• Machine cutters require a regular re-sharpening but the abrasion issues are not as visible as in previous versions of sulphur free.
• This latest version of sulphur free still remains a hard clay to work with which will affect productivity in model changes. I would estimate a 25% increase in time in manual labor on any model change.
• There is a certain amount of delamination of the clay in areas that have design tapes affixed, again proving there is still an adhesion issue.
• Painting the clay proved to be a none issue. Using the recommended stripcoat as a barrier no adverse effect was noticed.

Faber Clay Light (3rd Generation)

• Very soft compared to the Chavant ( Softer than I307 and Y2klay V130)
• Color is a light brown/mocha, needing dinoc film or highlighting film to spot check highlights. I would prefer a darker color.
• Surfaces very good with far less effort and abrasion to tools.
• As the clay is softer it is far more modeler and design friendly, good for quick changes.
• Lower heating temperature than Chavant.
• Compared to Chavant it has good adhesion properties although it still displays some delamination from tapes.
• Faber is certainly more on the oily side making it harder to apply tapes. Tapes tend to creep after a certain amount of time on the model surface, more than the clay by Chavant.
• More elasticity than Chavant with no visible cracking but to be fair a scale model cannot compare to a fullsize model.
• Machines very well with no cutter bounce.
• Like Chavant, requires an outside heat source to fully blend because of the higher wax content.
• Minimal delamination, even after tapes have been on for awhile
• Holds edges very well but would be susceptible to damage because it’s that much softer.
• Painting is no problem providing a water based primer is used. When painted with the stripcoat, which is a solvent based material a certain amount of reaction was noticed in the form of minute bubbles.

Kolb TecClay

• Of the three clays Kolb is very soft compared to Chavant and Faber. This version was known as TecClay Hard but still proved to be the softest of the three.
• very consistant in color and was not effected by oven age.
• Kolb was the lightest in weight compared to Chavant and Faber.
• The color was the lightest of the three being a yellow/brown which I’m not use to but it did have very good light/shadow properties.
• I found that it had a tendency to be on the dry side, crumbling between the fingers when manipulated.
• Edges can be a problem because of the dryness but once attained hold up very well.
• Less abrasive than Chavant, about the same as Faber and finishes very well.
• Easiest of the three clays for packing but does suffer from shrinkage if applying in a large thickness, all at once. Behaves better if applied in layers.
• Very crack resistant but only a scale model to evaluate.
• Machines well with little tool abrasion.
• Lower heating temperature than Chavant but like Faber is softer and less dense.
• Painting was not a problem with water based primer but like Faber reacted with the solvent based stripcoat with minute bubbles.

Well as you see, each clay has it’s high points and low points, with no one clay totally outshining the other. To pick one as the overall winner would be impossible, each one is still trying to perfect its product. If there is any rationale in picking the right clay then maybe geographical location would be the answer, go with the material that is produced locally, at least the transportation cost would be cheaper.

One of the main issues with this clay is after a few days in the oven it will get a crust that will never blend in with the rest of the billet. As in the normal procedure when packing a model, the billet is kneaded like dough to bring it to an even consistency before applying to the buck. What I am finding is the crust breaks up and gives little hard pieces in an otherwise creamy clay.

This is something that needs to be remembered, only have enough clay in the oven that is going to be used by the next day to avoid this crusting of the surface. This is especially important if adding to an already finished surface, otherwise the hard pieces will give a mottled effect to that surface.

The beauty of the current formula is, the oven can be refilled as clay is removed as it takes approximately three hours at 140°F to reach working temperature.

In this particular instance when the clay has hard crust particles, the clay is only good as a backing up material or underlying material which can then be covered with a fresh layer of clay. In the event of steeling, the crust particle surface gives the impression of going through sulphur particles with that very gritty sound, even though the filler used for this clay is something inert. To obtain the best finish to the model this should be avoided at all costs.

The other aspect of this Y2Klay is the hardness, it is so hard that the tools have to be sharpened more frequently than when using the previous I307 clay. The pressure on finger joints and wrist when packing is quite apparent by the aching of the joints at the end of the day, more so than any other clay that I have used.

I can understand the need for hardness in industrial clays especially as the majority of studios are now using milling machines to realize their first design impression but the modeling bucks still have to be prepared by hands on modelers. The majority of the resulting changes from the first milled model will also be dealt with by skilled clay sculptors. It will be interesting to see what percentage of sculptors suffer from arthritic problems at a later date from the constant loading of industrial clays.

To combat the aching joints I have resorted to a product called Glucosamine Chondroitin MSM by Nature’s Plus which is an advanced therapeutics cream. This is applied by hand and rubbed into the offending joints, it seems to work quite well but that may be purely a state of mind.

I have also found that there is a distinct lack of oils in this clay, making it difficult to soften by hand warming especially when filling small scars or holes in the model surface. It requires an additional trip to the oven or a nearby heat gun to soften it sufficiently. That said, the surfaces do finish crisply and edges hold without crumbling, no doubt time will tell to fully realize the potential of this clay.

Now this transition period was put on the fast track, there’s no point in prolonging the inevitable so I am now at a point where I can give you an overview of the product in question.

Y2Klay has been a product that Chavant has been perfecting over the last ten years and the main attributes are:

• Sulphur free, therefore reduces its corrosive ability.
• Less odor, no more smelly clothes through working with the clay.
• Light weight, a potential reduction in weight by 40% leading to less cost in shipping.
• Good working temperature (135°F or 57°C)
• Excellent milling properties

The manufacturer has assured me that the properties of this clay are very good and it will adhere to itself without additional heat. With that said, I’m always a little cautious when this type of statement is made, primarily because the inconsistencies that surround the manufacturing of the product. Even though there are numerous guidelines set for the vendors that supply the raw material the bandwidth may range from one extreme to the other so I’m sure there are plenty of missed heartbeats while producing each batch especially during these times of inconsistent oil prices.

For us to move forward with this new clay we first had to eliminate any cross contamination, several ovens were stripped down and totally cleaned out before reloading with Y2Klay and preheating the material to 135°F or 57°C. The intention was to model a complete model and see how it goes, no testing just get the job done. The application of the clay was easy enough, a very smooth consistency and it did adhere to itself with no problems but that was in the warm state, how will it perform when cold.

The next process was to mill the model via the Tarus mill, Chavant’s claim was true to form, the clay cut cleanly with no sticking to the milling cutter and no tearing of the clay. Small areas that were missing during the packing of the model were recovered with clay after first keying the surface with a clay rake. The clay blends in nicely but make sure you use some force when applying so that it becomes one with the underneath surface. Remilling of this area shows no sign of delaminating which is good, so far it is an improvement over the previous sulphur based clay.

Once the milling is finished it’s hand tools only, rakes, finishers and steels. The first impression is, it’s a harder clay than the I307, needing sharp tools to cut the surface smoothly without skidding over the top. Frequent sharpening on the diamond stone to hone the edge of the steels will no doubt require the teeth to be filed in on a regular basis. The surface of the clay cleans up crisp and the detail edges hold firm, no breaking away of the clay. This was an important factor for us, rebuilding edges is time consuming.

My overall impression of Y2Klay for this first project is, it performed exactly as stated, the working temperature is a little lower with no hotspots in the clay. It applies well even though it feels a little dry and adhesion is not a problem. For me this is a success but this was only a small project, the real test is to come, when we start on a fullsize model.

• TecClay is 100% sulphur free.
• TecClay has 40% less weight than normal clay.
• TecClay temperature stability is better than ordinary clay. Working temperature is 52 degrees Celcius.
• TecClay gives a perfect finish, no more irritating stroke traces or scratches.
• TecClay has edge stability, ideal for interiors with high detail.
• TecClay is perfect for CNC milling. The clay chips are dry and do not stick to the model.
• TecClay is oxidation free, homogenized and absolutely odorless.
• TecClay has excellent bonding capabilities.

Mark states that TecClay has been perfected over the past eight years giving it plenty of research history. My main concern as with all sulphur free clays is, they tend to be too dry and they do not adhere too well when having to make major model changes. Maybe it’s the change in oils and binders to make them mill friendly and light weight. The clay may not stick to the model when milled but by the same token the clay also doesn’t want to stick to itself unless an outside heating source is being used. I know that Kolb offer a portable clay heater that heats the clay to a depth of 20mm ( 3/4″ ) and this is obviously the reason for this particular piece of equipment. To heat a large area for a minor change can also have an adverse effect on the surrounding area, maybe even causing additional correction. Localized heating with a heat gun may be the answer but I am not a firm believer in this style of clay modeling.

With the majority of large corporations having to use sulphur free clay sooner than later, extra time will be needed to bring the clay up to a working temperature before adding additional clay, be it for changes or packing in preparation for milling. Preheating the clay on large models will be the only sure way of blending the clay for a seamless surface so as to avoid the likes of delamination and aerated surfaces.

In my working environment I have not used the Kolb TecClay and to become more familiar with the product I would be interested to hear from anyone who has. What is your experience with using this product, what are the good points, does it have any bad points?

What this means in terms to a design studio is, all new computer equipment installed will have less of a tolerance to the sulphur content of the clay accounting for a sooner than later break down of the computer circuit boards due to sulphur contaminant. Although this has not officially been confirmed it is suspect at two studios using sulphur containing clays, they have already reported computer failures shortly after installation. If this is indeed the case then we will find that computer warrantees will be invalid in the studio environment until the modeling clay used is totally sulphur free. The fact that Europe has taken this environmental stand it is only a matter of time before it becomes worldwide.

Ovens that have been retro fitted with a filtration system will still not contain the airborne sulphur that is attacking the now sensitive circuitry. Most of the clay suppliers are aware of this situation and do offer a sulphur free clay although the acceptancy of this product within the studios is still to be embraced. Suppliers such as Eberhard Faber have their version of sulphur free clay and you will find that the melting point for this clay to be 5-10 degrees C lower(41-50F) than the traditional sulphur based clay. Even with the aspect of being lighter in weight and more environmentally friendly the fact is these clays have not had as much research as the traditional sulphur based clays. Sulphur free research is probably 5-10 years in the making where the traditional clays have had decades of research to refer to. The bottom line is, consistency may become an issue.

Chavant a company that has over 100 years of experience in producing clay modeling products has its own variety of sulphur free clay called Y2-klay. This has a working temperature of 135 degrees F (57C), resistant to shrinking and cracking because of the higher wax content, easy to mill and does not stick to the milling cutter as bad as the traditional clays. Chavant has been pro-active in its research to provide a clay that is sulphur free and probably is the leader in as far as consistency for this type of product. Even so with todays climate within the petroleum companies, the reliability of by-products that are used to make the waxes is at risk causing never ending research to formulate a consistent blend for each batch of clay. The demand for these raw materials is such, that it is not guaranteed to be available when needed for the next run. These are the hurdles that todays clay suppliers have to face.

With the emergence of China and India as automotive hot spots, the use of certain ingredients will be in demand, possibly causing a run and shortage of key compounds in the production of clay and more than lightly an increase in cost in the near future. With the continual battle to gain market share by the automotive companies the use of automotive clays can only increase with each company trying to develop designs to draw in the fickle public, this in turn will no doubt put pressure on the already stretched clay suppliers for an increase in output.

Here in the United States it is common to use the material that is manufactured here, i.e. Chavant This material is manufactured in New Jersey and they have over 100 years of experience to pool on. There are two categories of clay, fine arts and industrial. The fine arts material is favored by free form sculptors such as special effect modelers and motion picture specialists. These clays tend to be softer than the industrial types and can normally be used at room temperature with no additional warming needed.

The industrial clays are harder and a warming oven is required to bring the clay up to a working temperature but once applied the clay is then worked with specialized tools to develop the design. These industrial clays come in various degrees of hardness, that is they still require warming but the hardness factor differs depending on the type you use.

In Europe a commonly used industrial clay is Faber. As with the Chavant clay this also needs to be heated in an oven to bring it to a workable temperature. The difference with this clay is it is sulphur free therefore has less of a smell compared to Chavant, even so chavant does manufacture a sulphur free clay.

Another product from Germany is Kolb clay. As with all industrial clays it needs to be heated in a warming oven to make it workable. Once it has cooled down it becomes hard enough to progress with your design. Each of these clays have their own merits for using them, it is normally the case of availability. Once again this is an odourless material that does not oxidize with age.

With all of these industrial clays, they are all suitable for use with modern milling equipment, such as the Tarus Clay Milling Machine, but equally, they are also at home with traditional hand tools as well.