molding and casting

Salvaging A Gelatin Mold. Not!

I mentioned earlier the failure of a plaster casting in a gelatin mold when I had to step back from work in the shop for a couple weeks during my vertigo incident (very much improved, only an occasional moment of lightheadedness), and my desire to try to salvage the warped, shrunken and hardened mold.

To manipulate and try to regain the utility of the mold I immersed it in hot water to see if that would do the trick. The experiment was both a complete failure and an enlightening success. Yes, the mold being manipulated started dissolving and slumping immediately, with, um, some loss of definition, resulting in it becoming a useless blob of goo.

That said it was elucidative of a correct direction in the overall enterprise, and enlightening to the future modifications. The fact that the mold could be manipulated by the hot water was instructive in confirming this strategy for a dried mold. That said it was immediately clear that the proportion of crosslinker in the original formulation was too low, so I will make a new mold with twice as much crosslinking additive. The mold had very little fungal attack so I know I am about at the right place for that additive.

So, sometimes ven failures keep you moving in the right direction.

Stay tuned.

When A Gelatin Mold Meets Vertigo

A couple months ago I made another gelatin mold and plaster casting in my efforts to refine that process, and test the proportions of preservatives for the gelatin.  At primary issue was keeping a mold viable for the longest period possible, to see how long the mold could be kept in a sealed container for future use.

The initial steps went perfectly.  Then my vertigo attack became manifest and I did not get back into the shop for more than two weeks.

Unfortunately for the mold and the plaster cast in it, it was just sitting on my bench and became desiccated and warped in the intervening fortnight.  Not good.  The mold became hardened and crushed the casting as it warped.

My next step is to see if the damaged mold can be resurrected with hot water or steam.  I’ll let you know what I find.

PS – Vertigo per se is gone, but I’ve had lingering dizziness which I describe as “being fuzzy around the edges.”  As long as there is no excess motion around me or I do not have to turn my head quickly I can manage.  Extensive and thorough medical examinations have yielded nothing yet.  I’m hoping it all goes away on its own.

Casting A Hairy Paw Foot

 

 

 

I have been doing molding and casting for almost four decades, and for the most part it has become a routine and enjoyable aspect of work in the studio.  But as with anything involving technology, technique, and “touch” there is room for it to go south, and I am in the midst of one such project.

Several weeks ago I was contacted by a blog reader asking me to cast a replica of a carved hairy paw foot he saw in an image I posted.  “Sure,” I said, and the misadventure was inaugurated.

My first step of creating a silicon mold was so straightforward I did not even bother to take pictures.  I figured I had just enough of the RTV rubber to make the mold and could cast it in plaster as requested.

Eeezy peeezy.

Only it turned out I had mis-estimated and I did not have enough of the molding rubber for the task, the liquid rubber barely covered the top knuckles of the foot, and was not thick enough for me to demold the foot without destroying the mold.  So, that time and material was down the crapper as a wasted effort.

Not to be dissuaded I turned to other mold-making options and struck on another molding material, Gelflex, a rubbery PVC molding material that is poured as a molten mass.  I’ve used it before with fairly good success, in fact one of the benefits of Gelflex is that is reusable.   When you are done with one application, you can just cut up and remelt the rubber for a subsequent use.  As long as you do not char the material it seems to have a near-infinite utility.

I set up the molding operation with my typical Lego box dam around the carved foot, which was anchored to a base board with sculpting clay.

I set up a Pyrex sauce pan on the hot plate and began to melt the material.  This was considerably more mass of Gelflex than I had tried using before (I had used it for replicating metal hardware in the past) and balancing the temperature so that it was hot enough to become liquid but not so hot as to char was a challenge.  It literally took three hours for me to get the temp/viscosity correct.

Even then I managed to chat some of the medium.

Then I poured the molten vinyl into the Lego box holding the carved leg in place with sculpting clay.

What could go wrong?

More Improvements to Gelatin Molds For Plaster Casting II

Armed with the knowledge and experience of recent attempts at making gelatin molds for plaster castings I charged forward with some new modifications to the formulation of the gelatin.

In this iteration I used the following recipe:

1 part 135 gws glue (dry granules)

1 part water, soaked overnight and cooked twice

3% glycerin

3% gelatin hardener

0.5% borate preservative

*Note: it is important to actually record the weight of the dry glue granules as the other additives are based on that number.*

Once the glue was well-cooked I added 3% glycerin and 35 of the hardener.  These numbers were based on the dry weight of the granules, in other words for 200 grams of glue granules I added ex poste 6 grams of glycerin and 6 grams of hardener.  I then added 1 gram (0.5%) of borate complex powder as a fungicide to extend the lifespan of the mold itself (not borax from the hardware store).

The working properties of the gelatin mold were excellent, although the time required for it to lose the requisite moisture  to become robust enough to use as a mold took longer than I expected.  I waiting a day before demolding from the pattern, two days would have been better.  But the resulting mold was extremely tough and utilitarian.

I cast plaster into the mold and demolded that the following day. Like the original demolding, longer would have been better.  Next time I will try 36 hours rather than~20.

The plaster casting was still pretty green since it took so long to slough off the water, so I placed it into a desiccation chamber to draw out the water.

The mold itself was placed into a sealed kitchen container with a damp sponge to maintain the water content of the mold, and thus its viability as a flexible and functioning plaster mold.

After three weeks I checked the mold and found a little bit of surface mold.  This was a useful observation.  The initial mold from many moons ago was a lump of goo after two weeks, this was still sort of viable after three.  I think next time I will jump the borate salt content to 0.75% or even 1.0% to see the result.

All in all I was very pleased with the progress being made, both conceptually and practically.

Stay tuned.

Where Did I Put That Stinking Knife Handle?

Recently I was sitting down ready to incise the pattern into the block that would become the pattern for the mold for making my soon-to-be-available Blend 31 block wax.  It was at that moment that I realized I had put the handles for my detail knives someplace for some reason I could not remember.  It was not that I had misplaced one of my handles, I could not find any of them, suggesting I had collected them for some purpose that I could no recall.  Fortunately they will be found as soon as my task is completed.

In the mean time, I needed a handle for the knife blades I needed to use.  So I made one.

Taking a piece of dowel stock from inventory I sawed a small slot with a fine Japanese back saw, inserted the blade into that and bound it with twisted copper wire, much in the same manner as quill brushes.  It worked just fine for the carving of the mat board that was the detailed surface of the block pattern.

An hour later I had the design incised into the surface and the block was ready for making the rubber mold.

 

And sure enough, the box with my micro tools was found right after this was finished.  Sigh.

More Improvements to Gelatin Molds For Plaster Casting I

Last month I brought together all the new information I had derived from the initial gelatin molds exercises to see if I could nail it on a more complex application.  For this project I used a pattern derived from a cast pot-metal satyr’s head mount from a 19th century pastiche of a 17th century French desk.  The hardware on the desk was cheezy and poorly finished (I was only interested in the desk itself as it was the earliest intact example of “mastic tortoiseshell”; another tale for another time).  This was probably a poor choice for a pattern because its level of “finishing” made it difficult to ascertain the ultimate success of the new mold and casting.

Just before this endeavor I was doing some winterizing and had a bolt-of-lightening stroke of inspiration.  As I was affixing the shroud around the window air conditioner with rope caulk I suddenly noticed the similarity of the rope caulk to the gaskets I made from modeling clay for my molding and casting.  Could it work the same way, but without the time involved in making the the initial gaskets?

I could hardly wait to get back home to try it out.

Fabulous!

I built the form-fitted Lego casting dam for the pattern/mold and quickly laid in a bead  of the rope caulk as the gasket on the inner edge of the underside, and pressed the assembly together.  The adhesion and squeeze-out was basically perfect.  Rope caulk is formulated to stick just enough to make it through the winter and then be peeled off with no residue in the spring.  Cleaning off the squeeze-out required only a pass with a boxwood sculpting tool configured  with a knife edge.

Suddenly I was in possession of a new technique to cut many minutes out of my pattern/casting dam set-up for the remainder of my working life.

It was now time to move forward with the modifications to the gelatin formulation and make the mold.

 

All A-buzz

Many times in the studio I need to shake something, just a teeny bit.

For example, when casting plaster or plaster like materials, such as ceramic media for lost-wax casting investment, it is sometimes necessary to tap on the mold container to dislodge air bubbles that all too often get lodged against the surface.  If they remain there the casting will be diminished, even ruined.  Many years ago I looked into getting a vibration table for buzzing the molds while the medium was still liquid, loosening the bubbles to rise to the surface.  After pricing the available devices I decided to go another route.

What could I use to cut the cost of a vibrating table down to near-zero?

Hearkening back 55 years to my times with Stan the Barber I recalled two things — Stan always had the latest comic books for the boys to read, a real treat for me because we were too poor to get them, and the tickle of the vibrating electric clippers on my neck when he was trimming up.  Could electric hair clippers be part of the answer?

The next time I ran across some clippers at the thrift store I decided to roll the dice with a buck-and-a-half for the clipper.  I combined the tool with some scraps of wood, two pieces of plumbing strap and a few screws.

Viola’.  A vibrating table for a couple bucks and a couple minutes.

Gelatin Molds For Plaster Casts III

With a number of data points in my hand it was time to give this  gelatin mold thing a trial run.  For the master pattern I selected one from my inventory of such things, an epoxy replica of a carved element.

I first affixed the pattern to a flat board using sulfur-free modeling clay as my gasket and adhesive.  I have used this method as a rock-solid tried-and-true technique for decades, the sulfur-free aspect is critical whenever the mold-making material is silicon rubber (sulfur inhibits the silicon rubber from setting), and I just use this as my default for every similar application.  I cleaned off the excess and brushed the thinnest possible coating of petroleum jelly onto the pattern to assure perfect separation, then dammed the pattern with a rectangle of Lego blocks.

For the gelatin mold material I used 192gws Standard glue, soaked overnight with the water level equal to the height of the glue in the glass jar.  I wanted the gelatin to be on the viscous side, remembering that all the water going in has to come out and there are shrinkage issues to consider with that.

Once the glue was cooked and ready, I added 3% of glycerin to it to serve as a plasticizer  followed by 2% protein hardener to crosslink the glue (both additions were by weight in proportion to the dry glue granules).  I had already learned to allow the glue to cool a bit before adding the hardener as higher temps make the crosslinking go too fast, turning the glue into an heterogeneous lumpy mixture.

Once everything was ready I simply poured the glue over the pattern until it stood proud of the surface by about 3/8″ and set it aside overnight.

The next day I dismantled the Lego dam and the rubbery block was just what I wanted, it peeled away from the pattern easily.  Clearly the hardener was imparting toughness from the git-go and the glycerin enhanced the flexibility of the still-swollen block.

 

I whipped up a batch of plaster and poured it into the gelatin mold with outstanding results.  Well, as outstanding as I could have expected given my impatience, which caused me to de-mold the casting too soon.  I should have waited 36 hours instead of 12; the high moisture content remaining in the gelatin mold retarded the setting of the plaster.

I immediately double bagged the gelatin mold to keep it from drying out, thinking the crosslinker would inhibit mold growth.

Not so much.  Two weeks later when I opened it to use it again it was something akin to a slimy special effect for a space alien movie.

Still more territory for improvement on the next try.

GroopShop 2018 – Day 1

Recently we traveled to Greater Atlanta to attend this year’s gathering of the Professional Refinisher’s Group, a/k/a “Groop,” and online forum to which I have belonged for almost twenty years.  Though initially a “virtual” community, we started assembling almost annually for the past 16 years.

Our hosts this year were the cooperative known as Southern Restorations whose large enterprise is steered by Brian Webster.

Note:  If you have even a passing interest in furniture finishing or restoration, you SHOULD be a member of Groop.  For further information on joining click here.  If you attended the HO Studley exhibit in Cedar Rapids IA you undoubtedly met some of our members, as most of the docents were volunteers from Groop.

Once again GroopShop was an invigorating time of fellowship and sometimes idiosyncratic conversations ranging from surviving running a small business in an esoteric marketplace to arcane discussions of technical subjects and all points in between (virtually all the members of Groop are some version of small businesses).  I know my interest was piqued on a regular basis throughout the three days, sometimes so much I forgot to take pictures..

After opening introductions and such the first demonstration of the event was for a low-impact abrasive cleaning system that was especially appealing to our members who undertake architectural work.  Were I a younger man living near the city trying to build a business, this is a device I would certainly consider obtaining.  The results were impressive, and I brought home a cleaned table leg to see how it finishes up.

Next came an excellent presentation on recent advances in waterborne coatings systems.  While I do not use much in the way of these products, if I had a commercial refinishing shop in this age of envirohysteria, I would.

Next came Dan and Tredway demonstrating the process by which they mold and cast replicas.  I especially enjoyed this not only because I have done so much of this, but because they use a very different product line/technology than I do.  (They are Smooth-On guys and I am a Polytek guy)  Somehow I wound up with the fancy eagle, and will probably paint and gild it and perhaps put it in next year’s Groop fundraising auction.  In the mean time I will experiment with making a gelatin mold plaster cast from it.

RandyB gave another inspiring talk about life in the antiques preservation trade.  His creativity knows no bounds.  His many years of caring for collectors’ and dealers has left him with a wealth of experience and knowledge.  I first met Randy while teaching at DCTC decades ago.

BobC gave his paean to oil finishes.  Intriguing.  I think there could be an intersection between them and polissoirs.

After dinner we held our annual Refinishing Jeopardy tournament, with host MikeM invoking Sicilian rules more than once.  Like most things Sicilian it is best not to ask too much about them.  I served as the adjudicating judge for any disputed answers.  Thanks to some curious scorekeeping the hilarity was sustained to the very end.

And thus endeth Day 1.

Gelatin Molds For Plaster Casts

A couple months ago I was sent a question about using gelatin molds for casting architectural plaster.  I had seen references to the technology in several of my old books but did not possess any that provided a decent description of the material or the process, so I noodled it a bit.  I’m not an architectural historian per se, so there might be plenty of old books with the exact information.

For the past almost forty years I have relied on silicone RTV molding rubber and never saw the need to broaden that horizon, but this question prompted me to undertake some exploring.  I am awfully glad I did as I now have another potent arrow in the quiver.

Of course at issue were several considerations.

  1.  The gelatin (hide glue) would need to be used in the semi-cured state, in other words after it had gelled and had not yet lost enough water to enter the more solid phase of a dried, cured mass.
  2. The gelatin mold had to be firm/flexible enough to actually cast plaster into it, then have the casting de-molded ex poste.
  3. The mold needed to be robust enough for repeated using.  The literature references using the molds dozens or even hundreds of times.
  4. Finally, the mold needed to remain viable while not becoming a giant fur-ball of mold.

Thanks to a timely failure of a tordonshell batch I gleaned the path to success, when combining that experience with some noumena from my wanderings into materials science.  The ultimate result was a high performance molding material that was also cheap.

The trek included a number of face palm moments in discovering new ways of working.

Stay tuned.