Coldglaze PRO 2 is one of the longest-serving products in the SylCreate range – and yet not many people outside of a specialist group of china, pottery and ceramic repair professionals know what the glaze is or what it does.
Until now. We are here to demystify Coldglaze and have recruited an expert in the art of using it to help us. Ian MacDonald is a restoration professional who has been using the Sylmasta Coldglaze PRO 2 System for years in his work and he has helpfully agreed to reveal the secrets to his trade.
But before we get to Ian’s restoration and glaze expertise, here is everything you need to know about the Coldglaze PRO 2 System for china, pottery and ceramic glaze and restoration.
What is Coldglaze PRO 2?
Used on its own, Coldglaze PRO 2 Gloss replaces the glaze effect on china, ceramic and pottery without requiring the use of heat. It has excellent non-yellowing characteristics, is water resistant and has high-strength surface adhesion.
Coldglaze can also be used to repaint patterns, either through mixing with pigments or oil colours. Various other products exist as part of the Coldglaze range for different finishes; Sylmasta Matting Agent S432 creates a matt finish when added to Coldglaze whilst CGW White Paste makes a high-quality, homogeneous white glaze.
Can anyone use Coldglaze PRO 2?
We recommend Coldglaze PRO 2 to professionals who have the necessary equipment and expertise to use the product. For example, when large quantities of glaze are mixed in industrial applications, then an extractor hood is needed – something which professionals have access to, but casual restorers may not.
That is not to say that beginners cannot use Coldglaze PRO 2. Small pottery and ceramic repairs are safe to carry out in a well-ventilated room and it is not too difficult to pick up the basics, providing you have the time and patience to master the art.
As with learning any new skill, it is best to practice before taking on the restoration of a priceless artefact so that you have the confidence and the knowledge to carry out a repair.
How to use Coldglaze PRO 2
Coldglaze PRO 2 is supplied in two parts with a mixing ratio of four parts resin to one part hardener by volume. Mixing takes place in a suitable, clean container, such as a small foil or glass dish.
The glaze is thoroughly mixed with a small stirrer. If the glaze needs to be thinned, then Sylmasta PT146 Thinners are added to the mix. Coldglaze PRO 2 can then be applied using either hand brush or airbrush with a pot life of up to eight hours under normal working conditions of 20℃.
If using a hand brush, we recommend a high-quality brush made from goat hair. To airbrush, add 20 percent by volume of thinners to obtain the necessary viscosity of glaze, which can then be applied to china, pottery or ceramic.
Adjustments to the airbrush mix can be made depending upon the desired finish. A wet film thickness of 50 – 60 microns will leave a dry film thickness of 25 microns.
At 20℃, Coldglaze PRO 2 has a surface dry of 10 to 15 minutes. A hard dry is achieved in 2 to 4 hours and full properties reached after seven days. Additional coats of Coldglaze must be applied either within 24 hours or after 90 hours.
The drying process can be sped up via force drying. A flash off period of 10 minutes should be allowed for the solvents to evaporate. Temperatures of 120℃ are recommended for 20 to 30 minutes when Coldglaze is used on ceramics and metal.
For plastic, particular care has to be taken to avoid deformation of the material. Typically, we recommend 60℃ for 2 to 3 hours.
Airbrush or hand brush?
When it comes to using Coldglaze to repaint, the experts at Lakeside Pottery have previously written about when is best to use airbrushing and when a hand brush is the more suitable option.
For general background colours and surface painting, they use an airbrush. It achieves a finer, translucent coating without any brush marks. The ultra-fine thickness blends seamlessly with areas that have not being restored or re-glazed.
Hand brushes are recommended when repainting highly detailed original patterns. To achieve the best finish, using a brush that is similar in type and stroke movement to that used when the original pattern was added is important.
If the restoration task involves repainting rather than merely glazing, then this is always the most time-consuming task. It is one that you will want to get right though as the success of the entire application can often hinge on it – so be sure to check out the Lakeside Pottery guide to painting and glazing repaired ceramic.
Improving the quality of a Coldglaze PRO 2 finish
Increasing the cure time of Coldglaze PRO 2 allows the glaze more time to flatten, giving a higher quality gloss finish to ceramic, china and pottery. A longer cure also improves adhesion of the glaze.
We recommend the use of Retarder for doing this. Retarder can also be used to reduce the overspray when airbrushing and reduce the cotton wool effect, particularly in warmer conditions. Retarder is added to PT146 Thinners at a ratio of 5 to 10 percent by volume.
Using Coldglaze PRO 2 with other glazes
Coldglaze PRO 2 can be used with other glazes, but we recommend using Barrier Coat before applying it to an existing glaze. This is to prevent a mixing of the two different glazes, which can have a detrimental impact on the item being restored.
Ian MacDonald’s restoration process
As promised, we spoke to one of our longest serving Coldglaze users to find out more about his restoration process. Ian was kind enough to take us through restoration from step one to step six, providing an invaluable insight for anyone wanting to restore or repair:
1) Start the process by establishing the extent of the damage and any previous repair work. It is also important to establish exactly what the client wants from the restoration.
2) Before the repair can begin, any previous repair materials need to be removed. These include glue, paint and muck. This is not always easy as, depending on the age of the piece, these materials might have been on the piece for 100 years.
3) Next, work out the order of reassembly of the pieces to avoid a potential lockout of the final piece. Assembling the item loosely using masking tape or similar can help to inform the process.
4) You can then decide the restoration method. Can the piece be glued all in one go using a clear epoxy adhesive? Or will it be better to reconstruct on a piece-by-piece basis with a setting period between each piece? This period can be anywhere between 20 minutes to an overnight cure, depending on the epoxy adhesive used.
5) Once the piece has been assembled, there may be minor gaps which need to be filled. This can be done with an epoxy putty like Milliput. In some cases, a new part may have to be fabricated using a mould from Godiva Wax or similar.
6) Finally, the piece is rubbed down and colour matched to the original. This is either done using acrylics or by mixing powdered pigments with Coldglaze PRO 2 which is applied via hand brush. A clear covering of Coldglaze either brush or spray applied is added to complete the restoration.
We would like to thank Ian MacDonald for his help with this article. Ian is available to carry out restorations of all kinds of items, and he can be contacted via email should you need an expert for your application.