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Etchings

Its not a question of coming up to look at my etchings ...... more of a question of what am I doing wrong with my etchings ....

I am etching brass (or attempting to) using a proprietary etch spray on positive resist which is cured under UV with the mask of the job and then developed, when the unmasked etch is supposed to wash away. ...... but doesn't.

All the usual issues of cleanliness and protection against light whilst applying the resist are being adhered to as are the suppliers recommendations for drying resist etc. The variables I have are amount of resist applied (too little/ too much) and the exposure to UV time (wattage/time/distance and possibly wavelength?) .... I use an 8 watt aquarium UV water filter lamp .....and lastly the film on which the image is printed.......it's overhead projector film.

When developed I get the right image defined sharply but the film seems to cast a shadow on the resist and it's this shadow that seems not to wash away when in the developer. Where the film is not covering the resist the resist washes away but not entirely cleanly needing a little encouragement with a very soft artist paint brush. That I can live with but getting the other to shift is impossible and finish with a crisp image.

It all points to the film being the problem but OH projector film is crystal clear so what gives?

All solutions earn nector points!!

Alan

Reply to
Alan Marshall
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Hi!

Sounds like a combination of a too thick layer of resist an too short exposure to UV-Light.

Try making the Layer of Photo-Resist thinner (but evenly distributed!) an doubling the Time of exposure.

Maybe ists worth considering ready-uv-resist-coated brass?

Look here:

formatting link
They sell a very thin brass for making solder print templates. I used it for making windows an buildings for railways in 1:87. It works like a charm. (Like any other consumable I ever got from this=20 company. No, I'm not connected to them in any way besides being a = satisfied customer.)

Michael.

Reply to
Michael Buchholz

One assumes that the film is less than perfectly clear to UV. Since your resist is a wash-away-after-exposure type, why not just expose for longer?

Mark Rand RTFM

Reply to
Mark Rand

Hi!

Sounds like a combination of a too thick layer of resist an too short exposure to UV-Light.

Try making the Layer of Photo-Resist thinner (but evenly distributed!) an doubling the Time of exposure.

Maybe ists worth considering ready-uv-resist-coated brass?

Look here:

formatting link
They sell a very thin brass for making solder print templates. I used it for making windows an buildings for railways in 1:87. It works like a charm. (Like any other consumable I ever got from this company. No, I'm not connected to them in any way besides being a satisfied customer.)

Dear Michael

The thin brass sheet and Bungard's sensitised anodised aluminium sheet looks really useful stuff. I looked on the Bugard website but could not see much real information (size/price etc)

Do you know whether its easily available in the UK?

Ian

Reply to
Ian Phillips

amount of

You will find tracing paper is actually beter (and somewhat cheaper) than over head projector film. I'm using '90gsm A4 Goldline Tracing Paper" and it works a treat on my laser printer. Print you image so that the printing is in contact with the resist layer when exposed to us (rather than through the sheet), so no uv can spread as it passes through.

AWEM

Reply to
Andrew Mawson

I would guess the problem is with the lamp; most resists are sensitive to

350 to 400nm (UVA), sterilising tubes (with a clear envelope) produce light with a wavelength of 253nm (UVC). You need to use a blacklight type tube which produces mainly UVA. A word of caution, sterilising tubes can cause severe sunburn and damage to the cornea if you are exposed to the output for even a short period of time. Martin
Reply to
Martin Whybrow

Sorry, not the slightest Idea about a UK supplier, the Stuff IS pricey, = tough. I seem to remember about 150Euros per 1000mm*500mm*1,5mm Aluminium sheet = in Black. I Don't have a price for the brass in mind, sorry.

But give them a call, they are very willing to help. Every time i ordered this black aluminium sheet to be cut in tiny (150mm = by 30mm) pieces, they would say:" We cant do smaller cuts than 100mm, employee = saftey issue. But their Boss said every time: "I'll do it myself, You will get Your = tiny pieces. (my ex-employer used the small cutoffs for Bar-code-marking the = Flight-cases, as they were a Stage-Rental-Company and laser-printout-markings tended to = last only=20 one Job ;-)

Michael.

Reply to
Michael Buchholz

I had the same problem years ago. In the end, the solution was to silkscreen the design on to brass. I used Ulano Poly Blue, and a blockout solution to cover areas outside the image to be printed. Kodak graphic arts film was used to make the master negative/positive to expose the Poly Blue. The silkscreen film was available as a free sample. For model making, one sample kit will last for years.

Steve R.

Reply to
Steve R.

Thanks for all the replies guys...... lots of food for thought. Alan

Reply to
Alan Marshall

Ahha ...... checked my UV tube and it is marked UVC so have ordered a Blacklight tube for UVA and we will see the results from that.

Alan

Reply to
Alan Marshall

Used the new lamp and there was a marked improvement. However the shadow effect is still there to a lesser degree. I think the shadow is caused by the matt surface finish on the OHP film onto which the ink is printed. Tried to print onto high gloss film that has no matt surface and the inkjet printer ink does not dry out properly and also does not give a sharp edge if the film is at all non clean. I guess a laser printer or toner type copy printer must be used.

More experiments needed.

Alan

Reply to
Alan Marshall

In message , Alan Marshall wrote

Try printing the image reversed then lay the printed side onto the resist coated plate, that way the image should be as sharp as possible.

Reply to
Roger Smith

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